Cheesy Collard Greens Gratin: A Southern-Inspired Baked Casserole

Prep Time: 30 minutes | Cook Time: 30 minutes | Servings: 8

The culinary landscape of the South is defined by its deep traditions and ability to turn simple vegetables into magnificent, soulful dishes. While collard greens are traditionally simmered low and slow with smoked pork until buttery soft, this recipe elevates the beloved Southern staple into a rich, creamy, and undeniably luxurious baked casserole: the Cheesy Collard Greens Gratin. This dish takes the savory, slightly earthy flavor of cooked collards and bathes them in an incredibly decadent three-cheese béchamel sauce, topped off with a crunchy, golden panko crust. Forget mushy greens; this is a sophisticated, crowd-pleasing side that deserves a spot at your holiday table or next Sunday supper.

Our goal with this Cheesy Collard Greens Gratin is to combine the deep, comforting flavors of the South achieved through slow cooking the greens with aromatics and a hint of smoke with the rich, textural excellence of French cuisine (the gratin technique). The result is a dish that is simultaneously familiar and exciting, offering a stunning contrast between the tender, slightly spicy greens and the crisp, bubbling cheese topping. If you’ve been searching for a way to convert collard green skeptics, or simply want a remarkable side dish that steals the show, you’ve found your new favorite recipe.

Why You’ll Love This Cheesy Collard Greens Gratin

This recipe for Cheesy Collard Greens Gratin isn’t just about making a side dish; it’s about crafting a centerpiece of flavor and texture. Many traditional vegetable sides often fall flat, but this gratin is built on three layers of irresistible appeal that ensure every bite is memorable. The marriage of classic Southern seasoning with a luxurious European technique creates a flavor profile that is complex, comforting, and absolutely addictive.

The Perfect Marriage of Flavor and Texture

What sets this gratin apart is the stunning contrast it offers. You start with the depth of the collards themselves slightly bitter, earthy, and perfectly tender thanks to the long simmer in broth infused with smoked paprika and garlic. This foundation ensures the dish retains its Southern soul. Then, we introduce the creamy element. The rich béchamel, carefully prepared with warm milk and a proper roux, is transformed into a majestic cheese sauce by incorporating sharp cheddar and nutty Gruyère. These cheeses melt seamlessly, enveloping the greens in a velvety cocoon.

Finally, we achieve textural perfection with the crispy panko topping. Unlike standard breadcrumbs, panko delivers a truly shattering crunch. When mixed with melted butter and a combination of cheddar and salty Parmesan, it bakes into a golden cap that provides a delightful textural break from the creamy interior. This textural dynamic creamy base, tender filling, crispy top is the secret ingredient to why people fall in love with this Cheesy Collard Greens Gratin.

A Comfort Food Classic, Elevated

While mac and cheese or potato casseroles often dominate the comfort food scene, the Cheesy Collard Greens Gratin offers a surprisingly healthy yet equally satisfying alternative. It appeals to those who crave deep, savory flavor without the heavy starch load of pasta or potatoes. It’s the ultimate Southern comfort food, reimagined for modern gatherings. This dish is hearty enough to serve as a vegetarian main course alongside a light salad, but it truly shines as a decadent side dish for roasted meats, barbecue, or holiday feasts.

Furthermore, the smoky undertones provided by the smoked paprika and the gentle warmth from the optional red pepper flakes cut through the richness of the cheese sauce, ensuring the dish is never cloying. It’s a beautifully balanced bite that highlights the versatility of collard greens. If you’re a fan of comforting, baked dishes like Creamy Green Bean Casserole with Cream Cheese, you will certainly appreciate the depth and richness of this Cheesy Collard Greens Gratin.

Why You Should Try This Recipe Today

Trying the Cheesy Collard Greens Gratin is a culinary adventure that promises big rewards for relatively little effort, especially when compared to complex holiday baking or slow-cooked mains. If you are aiming for a show-stopping side that uses seasonal ingredients and brings a comforting warmth to the table, this recipe is a must-make. It solves the common dilemma of finding vegetable sides that are both healthy (collards are packed with nutrients!) and irresistibly decadent.

Ideal for Gatherings and Meal Prep

This recipe is perfectly scaled to serve eight, making it an ideal choice for dinner parties, potlucks, Thanksgiving, or Christmas. Unlike many sides that require last-minute assembly, the Cheesy Collard Greens Gratin is highly flexible. You can prepare the cooked collards and the cheese sauce a day in advance. Simply store them separately, assemble the gratin the next day, add the topping, and bake. This makes managing cooking timelines for large events significantly easier, allowing you to focus on the main course while knowing your spectacular side is ready to go.

The rich, savory nature of this baked side also means it reheats beautifully, making it excellent for next-day leftovers. The smoky collards and cheesy sauce meld even further overnight, deepening the flavor profile. Preparing dishes like this Cheesy Collard Greens Gratin in advance is an essential strategy for stress-free entertaining.

Mastering the Art of the Roux

One of the most valuable kitchen skills you will gain from preparing this recipe is mastering the béchamel sauce, or roux-based white sauce. The instructions are detailed to ensure your sauce is lump-free and perfectly creamy. A successful béchamel is the foundation of the gratin’s rich texture. Once you have mastered this sauce for the Cheesy Collard Greens Gratin, you open up a world of creamy cooking possibilities, from homemade mac and cheese to creamy vegetable casseroles. This recipe builds culinary confidence!

For those looking for other hearty, comforting side dishes, consider pairing this with a main course that complements its richness, or trying another comforting baked dish like our Cheesy Vegetable Casserole. Incorporating this Cheesy Collard Greens Gratin into your repertoire guarantees a delicious and unique addition to any menu. This dish offers a compelling alternative to traditional baked sides, proving that greens can indeed be the star of the show. The smoky, earthy depth of the collards is perfectly counterbalanced by the bright, sharp notes of the cheddar and Gruyère, creating a truly unforgettable flavor profile.

Ingredients and Necessary Utensils for Cheesy Collard Greens Gratin

Success in making the perfect Cheesy Collard Greens Gratin hinges on two things: using high-quality ingredients (especially fresh, sharp cheese) and ensuring you have the right tools for the job. Do not underestimate the need to drain the collards thoroughly a watery gratin is the only thing standing between you and cheesy perfection.

Essential Ingredients Checklist

We divide the ingredients into three key stages: the collard greens preparation, the rich béchamel cheese sauce, and the crispy topping. Paying attention to the quality of your cheese will significantly impact the final texture and flavor of the Cheesy Collard Greens Gratin.

For the Collard Greens:

• 2 large bunches (about 3 pounds) fresh collard greens: Look for firm, vibrant green leaves. Proper washing and slicing are essential.
• 2 tablespoons olive oil: Used for sautéing the aromatics.
• 1 medium yellow onion, finely diced: The sweet base of flavor for the greens.
• 4 cloves garlic, minced: Adds depth and aromatic warmth.
• 1 cup chicken or vegetable broth (low sodium): Provides moisture and flavor for simmering the greens until tender.
• 1/2 teaspoon smoked paprika: Absolutely crucial! This adds the necessary smoky, Southern flavor without needing bacon or ham hocks.
• 1/4 teaspoon red pepper flakes (optional): Highly recommended for a gentle, warming heat that balances the richness of the cheese.
• Salt and freshly ground black pepper, to taste: Seasoning the greens adequately ensures maximum flavor before they meet the cheese sauce.

For the Cheese Sauce (Béchamel):

• 4 tablespoons unsalted butter: The fat component of the roux.
• 1/4 cup all-purpose flour: The thickening agent (the base of the roux).
• 3 cups whole milk, warmed: Using warm milk prevents the roux from seizing and makes whisking easier. Whole milk provides the richest texture for the Cheesy Collard Greens Gratin.
• 1/4 teaspoon ground nutmeg: A classic addition to béchamel that adds a subtle, earthy warmth, balancing the sharp cheese.
• 1 teaspoon dry mustard powder: This doesn’t make the sauce taste like mustard; instead, it acts as a flavor enhancer, intensifying the savory, sharp notes of the cheddar cheese.
• 1 cup sharp cheddar cheese, freshly grated (reserve 1/2 cup for topping): Freshly grated cheese melts much smoother than pre-shredded cheese (which often contains anti-caking agents). Sharp cheddar provides that essential tanginess.
• 1 cup Gruyère or Monterey Jack cheese, freshly grated: Gruyère offers a beautiful nuttiness and superior melt quality. Monterey Jack is a milder, easy-melting alternative if Gruyère is unavailable.

For the Crispy Topping:

• 1 cup panko breadcrumbs: Panko is non-negotiable for a truly crispy crust; standard breadcrumbs will result in a softer topping.
• 2 tablespoons unsalted butter, melted: To bind the topping and help it brown beautifully.
• 1/2 cup reserved grated sharp cheddar cheese: Mixing cheese into the topping ensures every part of the gratin has that cheesy pull.
• 1/4 cup grated Parmesan cheese: Adds a salty, umami kick to the crust.

Recommended Tools and Utensils

Having the right equipment ensures a smooth cooking process, particularly when dealing with the volume of collard greens and the precision required for the béchamel sauce.

• Large Dutch Oven or Deep Skillet: Necessary for sautéing the three pounds of collard greens. A pot with a lid is essential for the simmering phase.
• 9×13 Inch Baking Dish: The standard size for baking the gratin. Ensure it is lightly greased.
• Medium Saucepan: Specifically for preparing the béchamel cheese sauce.
• Whisk: Essential for making the roux and the béchamel. A wire whisk ensures a perfectly smooth, lump-free sauce, which is critical for the success of your Cheesy Collard Greens Gratin.
• Sharp Knife and Cutting Board: For preparing the collards (chiffonade technique) and dicing the onion.
• Colander or Sieve: Crucial for draining the cooked greens. You must press out as much excess liquid as possible after cooking to prevent a watery casserole.
• Measuring Cups and Spoons: For precise ingredient ratios.
• Large Mixing Bowl: Used to combine the drained collards and the cheese sauce before layering.

The success of the Cheesy Collard Greens Gratin relies heavily on the quality and preparation of the collard greens. Taking the time to properly wash, strip, and thinly slice the greens (the chiffonade) ensures they cook evenly and integrate seamlessly with the creamy sauce, rather than having large, chewy pieces. Remember, fresh ingredients and careful preparation techniques will yield the most spectacular and sought-after Southern-inspired side dish.

Detailed Recipe Steps for the Ultimate Cheesy Collard Greens Gratin

Follow these instructions meticulously, paying close attention to the steps involving draining the greens and preparing the roux, as these are the two main factors that determine the final quality of the Cheesy Collard Greens Gratin.

1. Prepare the Collard Greens: The Foundation of Flavor

Thorough washing is paramount, as collards can hold grit. Thoroughly wash the collard greens under cold running water. Next, prepare the leaves: Strip the tough leaves from the thick central ribs. While the ribs can be cooked, they take longer and can be chewy in a gratin, so we discard them for this recipe. Stack several leaves neatly on top of one another, roll them tightly like a cigar, and slice them across the roll into thin ribbons (this technique is known as a chiffonade). Aim for slices about 1/4 to 1/2 inch thick. Set the sliced greens aside.

2. Sauté the Aromatics and Cook the Greens

Preheat a large Dutch oven or deep skillet (the largest pot you have) over medium heat and add the 2 tablespoons of olive oil. Add the diced yellow onion and sauté gently for 5 to 7 minutes until softened and translucent, being careful not to brown them. Next, add the minced garlic and sauté for just 1 minute until highly fragrant. Do not allow the garlic to brown, or it will turn bitter. Add the prepared collard greens to the pan. Because of the volume, you will need to do this in batches, stirring until they wilt down slightly before adding the next batch. Pour in the broth, smoked paprika, and red pepper flakes (if using). Stir well to combine the seasoning. Cover the pan, reduce the heat to low, and simmer the greens for 15 to 20 minutes, or until tender. The goal is soft, but not mushy, greens.

🚨 Crucial Tip: Drain, Drain, Drain! Once cooked, transfer the collards immediately to a colander or sieve. You must drain the greens exceptionally well to remove excess liquid, ensuring they are as dry as possible. Press the greens against the sieve with the back of a spoon to force out moisture. If the greens are too wet, the final Cheesy Collard Greens Gratin will be loose and watery. Season the drained collards with salt and pepper, then transfer the greens to a large mixing bowl.

3. Prepare the Béchamel Cheese Sauce

While the greens are draining and cooling slightly, prepare the sauce. Melt the 4 tablespoons of butter in a medium saucepan over medium heat. Once melted and foamy, whisk in the flour to create a smooth paste (a roux). Cook the roux, stirring constantly, for 1 to 2 minutes. Cooking the roux is essential to eliminate the raw flour flavor. Slowly whisk the warm milk into the roux, pouring in a steady, thin stream to prevent lumps. Continue whisking as the sauce heats. Bring the sauce to a gentle simmer, whisking frequently until it thickens sufficiently to coat the back of a spoon (about 5 to 8 minutes). Reduce the heat to low once thickened.

4. Finish the Sauce and Assemble the Gratin Base

Remove the saucepan from the heat immediately after it has thickened. Stir in the nutmeg and dry mustard powder. Add the Gruyère and 1 cup of the sharp cheddar cheese (remember to reserve the remaining 1/2 cup for the topping). Stir vigorously until the cheeses are completely melted and the sauce is smooth, creamy, and velvety. Taste the sauce and adjust seasonings with salt and pepper as needed it should be savory and well-seasoned, as the cheese is the only liquid flavoring the gratin mixture. Pour about three-quarters of the finished cheese sauce over the drained collard greens in the mixing bowl and stir thoroughly to coat every piece of the greens evenly. This forms the cheesy base for your Cheesy Collard Greens Gratin.

5. Layer and Top the Gratin

Preheat the oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish. Spread the cheesy collard green mixture evenly into the prepared baking dish. Use a spatula to level the surface. Pour the remaining cheese sauce over the top of the greens. This layer of sauce acts as a barrier and ensures the topping adheres beautifully and the center remains moist.

Prepare the crispy topping: In a small bowl, combine the panko breadcrumbs, the 2 tablespoons of melted butter, the reserved 1/2 cup of sharp cheddar, and the grated Parmesan cheese. Toss the mixture thoroughly until the panko breadcrumbs are lightly coated and sticky with the butter and cheese. Sprinkle this topping mixture evenly over the entire surface of the Cheesy Collard Greens Gratin. Ensure even distribution for maximum crispness.

6. Bake and Serve the Cheesy Collard Greens Gratin

Place the gratin in the preheated oven on the middle rack. Bake for 25 to 30 minutes, or until the sauce is deeply bubbly around the edges and the breadcrumb topping is golden brown and exceptionally crisp. Monitor the topping closely during the last 10 minutes; if it browns too quickly, you can loosely tent the dish with aluminum foil.

Remove the Cheesy Collard Greens Gratin from the oven. Allow it to rest for a crucial 10 to 15 minutes before attempting to scoop and serve. This resting time allows the cheese sauce to cool slightly and set up, making the gratin hold its shape better upon serving. Serve warm and enjoy this incredible Southern comfort food.

Tips, Tricks, and Delicious Variations

While the basic recipe for Cheesy Collard Greens Gratin is perfect as written, there are many ways to tailor this dish to dietary needs or personal preferences, ensuring this side dish becomes a year-round staple in your kitchen.

Ingredient Swaps and Flavor Boosters

• Cheese Alternatives: If Gruyère is difficult to find, use Monterey Jack or white cheddar for a smooth melt. For an extra sharp, salty kick, substitute the Gruyère with half smoked Gouda and half Provolone.
• Adding Meat (The Southern Classic): To lean into traditional Southern flavor, sauté 1/2 cup of finely diced, rendered bacon, ham hock, or smoked turkey along with the onions in Step 2. This infuses the greens with deeper smoky flavor and makes the Cheesy Collard Greens Gratin even heartier.
• Spice Level: If you love heat, increase the red pepper flakes to 1/2 teaspoon, or add a dash of hot sauce (such as Texas Pete or Tabasco) to the cheese sauce before mixing it with the greens.
• Herb Infusion: Add 1 teaspoon of dried thyme or a tablespoon of finely chopped fresh parsley or chives to the collards mixture before baking for a fresh, herbaceous note.

Dietary and Lifestyle Variations

The beauty of a baked casserole like this Cheesy Collard Greens Gratin is its adaptability.

• Gluten-Free Gratin: Easily convert this recipe by substituting the all-purpose flour in the béchamel with a measure-for-measure gluten-free flour blend. For the topping, ensure you use gluten-free panko breadcrumbs, which are widely available.
• Low-Carb Option: Omit the flour in the béchamel and replace it with 1/2 teaspoon of xanthan gum whisked into the melted butter before adding the milk. This will thicken the sauce without carbohydrates. For the topping, skip the panko entirely and mix the reserved cheddar and Parmesan with crushed pork rinds or finely chopped pecans for a crunchy, flavorful, low-carb crust.
• Vegan/Dairy-Free Version: Replace the butter with vegan butter sticks (e.g., Miyoko’s or Earth Balance). Use unsweetened plant-based milk (like oat or soy) instead of dairy milk. Substitute the cheddar and Gruyère with high-quality, meltable vegan cheese shreds, ensuring you use a sharp variety for maximum flavor impact in the Cheesy Collard Greens Gratin.

Troubleshooting Common Mistakes

1. My Gratin is Watery: This is the most common issue. The greens were not drained sufficiently after simmering. The absolute key to a firm, non-watery gratin is squeezing out as much liquid as possible from the cooked collards. If your greens are still damp, they will leach water into the béchamel during baking.
2. My Sauce is Lumpy: This means the roux wasn’t cooked properly, or the milk was added too quickly and wasn’t warm enough. Always add the warm milk slowly to the roux while whisking vigorously and constantly. If lumps occur, strain the finished cheese sauce through a fine-mesh sieve before mixing it with the greens.
3. The Topping Burned: If your oven runs hot, or if the top browns very quickly (in less than 15 minutes), the breadcrumbs may burn before the interior is bubbly hot. Loosely tent the gratin with aluminum foil for the last 10–15 minutes of baking.

Whether you’re serving this alongside barbecue or incorporating it into a holiday spread with other classic comfort foods like Loaded Potato Soup, the Cheesy Collard Greens Gratin is guaranteed to be a hit. Its deep flavor profile and comforting texture make it an irresistible vegetable side.

Nutritional Values and Health Benefits of Cheesy Collard Greens Gratin

While the word “cheesy” often implies indulgence, collard greens themselves are nutritional powerhouses. This recipe, when enjoyed in moderation as a side dish, provides significant nutritional benefits, primarily derived from the leafy greens.

Estimated Nutritional Information (Per Serving, based on 8 servings):

Note: These values are estimates and vary based on exact cheese and milk fat content. The high fat content reflects the use of whole milk, butter, and multiple cheeses.

The Power of Collard Greens

Collard greens are classified as a cruciferous vegetable, part of the same family as kale and Brussels sprouts, and they are incredibly nutrient-dense. Even after simmering, they retain many of their health benefits:

• Vitamin K Champion: Collard greens are one of the best sources of Vitamin K, essential for blood clotting and crucial for bone health. A single serving of the greens base in this Cheesy Collard Greens Gratin often exceeds the daily recommended intake.
• High in Fiber: The high fiber content in collard greens aids in digestive health, promotes satiety, and helps stabilize blood sugar levels. This fiber also helps balance the richness of the cheese sauce.
• Antioxidants and Anti-Inflammatory Properties: Collards contain potent antioxidants, including carotenoids (like lutein and zeaxanthin), which are vital for eye health. Their anti-inflammatory compounds contribute to overall cellular health.
• Calcium and Vitamin C: They are a good source of plant-based calcium and Vitamin C, which supports the immune system and collagen production.

Balancing Decadence with Nutrition

While the béchamel sauce makes this Cheesy Collard Greens Gratin an indulgence, the sheer volume and density of the collards ensure that each serving packs a substantial nutritional punch. By incorporating sharp, flavorful cheeses like cheddar and Gruyère, we achieve maximum flavor payoff without needing excessive amounts of fat or sugar often found in other casserole recipes.

We use smoked paprika for flavor rather than relying solely on processed meats, reducing overall sodium and fat compared to traditional preparations involving a ham hock, making this a healthier, albeit still decadent, option for a Southern side. Enjoying a small portion of this flavorful Cheesy Collard Greens Gratin means you are nourishing your body with essential vitamins while satisfying that craving for hearty, soulful comfort food.

Frequently Asked Questions (FAQs) about Cheesy Collard Greens Gratin

Conclusion: The Ultimate Southern Side Dish

The Cheesy Collard Greens Gratin is more than just a side dish; it’s a celebration of Southern tradition enhanced by classic culinary technique. By transforming the sometimes overlooked collard green into a baked casserole masterpiece, we create a dish that is rich, comforting, and visually stunning. We’ve layered earthy, smoky flavors with the velvety smoothness of a three-cheese béchamel, all crowned by the perfect golden, crisp panko crust.

This recipe provides a wonderful opportunity to introduce collard greens to new palates, proving that these hearty leaves are capable of profound deliciousness when treated with the right amount of cheese and butter. Whether you are hosting a holiday feast, planning a Sunday dinner, or simply looking to elevate your weeknight meals, this gratin delivers on every promise of comfort and complexity. The sharp cheddar and nutty Gruyère perfectly cut through the slight bitterness of the greens, ensuring a balanced and addictive flavor profile.

Take pride in the skills you developed while mastering the roux and achieving the perfect tenderness of the greens. The effort is rewarded tenfold when you pull that bubbly, golden Cheesy Collard Greens Gratin from the oven. Don’t let this recipe remain on your “to-try” list; grab those fresh collards, start grating your cheese, and prepare to delight your guests with this extraordinary Southern-inspired casserole. If you enjoyed this creamy dish, you might also love our recipe for Creamy Cajun Chicken Pasta, which utilizes similar creamy sauce techniques.

We encourage you to try the Cheesy Collard Greens Gratin this week and share your experience below! What cheeses did you use? Did you add the optional red pepper flakes? Your feedback helps us build a thriving community of comfort food enthusiasts.

CHEESY COLLARD GREENS GRATIN: A SOUTHERN-INSPIRED BAKED CASSEROLE

This decadent Southern-inspired casserole takes classic collard greens and bakes them in a rich, creamy cheese sauce (béchamel) with a crispy panko-cheddar topping. It's the perfect savory side dish for holidays or any comfort meal.

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Prep Time 30 minutes mins

Cook Time 30 minutes mins

Total Time 1 hour hr

Servings: 8 servings

Course: Casserole, Side Dish

Cuisine: American, Southern

Calories: 380

Ingredients Equipment Method Notes

Ingredients

  

For the Collard Greens

• 2 large bunches (about 3 pounds) fresh collard greens
• 2 tablespoons olive oil
• 1 medium yellow onion finely diced
• 4 cloves garlic minced
• 1 cup chicken or vegetable broth low sodium
• 1/2 teaspoon smoked paprika
• 1/4 teaspoon red pepper flakes optional, for heat
• to taste Salt and freshly ground black pepper

For the Cheese Sauce (Béchamel)

• 4 tablespoons unsalted butter
• 1/4 cup all-purpose flour
• 3 cups whole milk warmed
• 1/4 teaspoon ground nutmeg
• 1 teaspoon dry mustard powder
• 1 cup sharp cheddar cheese, freshly grated reserve 1/2 cup for topping
• 1 cup Gruyère or Monterey Jack cheese, freshly grated

For the Crispy Topping

• 1 cup panko breadcrumbs
• 2 tablespoons unsalted butter, melted
• 1/2 cup reserved sharp cheddar cheese grated
• 1/4 cup grated Parmesan cheese

Equipment

• Large Dutch Oven or Deep Skillet
• Medium saucepan
• 9x13 inch baking dish
• Large Mixing Bowl

Method

 

Preparation Steps

1. Prepare the Collard Greens: Thoroughly wash the collard greens. Strip the leaves from the thick central ribs. Stack several leaves on top of one another, roll them tightly like a cigar, and slice them into thin ribbons (a chiffonade). Set the greens aside.
2. Sauté the Aromatics and Cook the Greens: Preheat a large Dutch oven or deep skillet over medium heat and add the 2 tablespoons of olive oil. Add the diced yellow onion and sauté for 5 to 7 minutes until softened and translucent. Add the minced garlic and sauté for 1 minute until fragrant. Do not allow the garlic to brown. Add the prepared collard greens to the pan in batches, stirring until they wilt down slightly before adding the next batch. Pour in the broth, smoked paprika, and red pepper flakes (if using). Cover the pan, reduce the heat to low, and simmer the greens for 15 to 20 minutes, or until tender. Once cooked, drain the collards well to remove excess liquid, ensuring they are as dry as possible. Season with salt and pepper, then transfer the greens to a large mixing bowl.
3. Prepare the Béchamel Cheese Sauce: While the greens are simmering, prepare the sauce. Melt the 4 tablespoons of butter in a medium saucepan over medium heat. Whisk in the flour to create a smooth paste (a roux). Cook the roux, stirring constantly, for 1 to 2 minutes to cook out the raw flour flavor. Slowly whisk the warm milk into the roux, pouring in a steady stream to prevent lumps. Bring the sauce to a gentle simmer, whisking frequently until it thickens sufficiently to coat the back of a spoon (about 5 to 8 minutes). Reduce the heat to low.
4. Finish the Sauce and Assemble the Gratin Base: Remove the saucepan from the heat. Stir in the nutmeg and dry mustard. Add the Gruyère and 1 cup of the sharp cheddar cheese (reserving the remaining 1/2 cup for the topping). Stir until the cheeses are completely melted and the sauce is smooth. Taste the sauce and adjust seasonings with salt and pepper as needed. Pour about three-quarters of the cheese sauce over the drained collard greens in the mixing bowl and stir thoroughly to coat every piece of the greens evenly.
5. Layer and Top the Gratin: Preheat the oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish. Spread the cheesy collard green mixture evenly into the prepared baking dish. Pour the remaining cheese sauce over the top of the greens. In a small bowl, combine the panko breadcrumbs, 2 tablespoons of melted butter, the reserved 1/2 cup of sharp cheddar, and the grated Parmesan cheese. Toss the mixture until the breadcrumbs are lightly coated in the butter and cheese. Sprinkle this topping mixture evenly over the entire surface of the collard greens.
6. Bake and Serve: Place the gratin in the preheated oven and bake for 25 to 30 minutes, or until the sauce is bubbly around the edges and the breadcrumb topping is golden brown and crisp. Remove the gratin from the oven and allow it to rest for 10 to 15 minutes before serving. This resting time helps the gratin set up, making it easier to scoop and serve.

Notes

Ensure you drain the collard greens very thoroughly after simmering. Excess moisture will thin out the cheese sauce and prevent the gratin from setting properly. For an extra smoky flavor, you can substitute a tablespoon of the olive oil for bacon grease when sautéing the onions.