The Ultimate French Onion Broccoli Cheese Casserole: A Decadent Comfort Food Fusion

If you thought broccoli cheese casserole was the peak of creamy, comforting side dishes, prepare for an absolute culinary revelation. We are taking the classic, earthy green vegetable bake and marrying it with the rich, savory depth of classic French onion soup. The result is the show-stopping, deeply flavorful French Onion Broccoli Cheese Casserole.

This isn’t your grandma’s standard weeknight side dish. This casserole elevates comfort food to an art form, driven by the secret weapon of French cuisine: slowly, lovingly caramelized onions. These golden, jammy jewels provide an unmatched layer of umami and sweetness that melts into a velvety Gruyère and sharp cheddar cheese sauce. Layered with perfectly tender-crisp broccoli florets and topped with crispy, toasted croutons, this casserole offers an experience that is luxurious enough for a holiday meal but undeniably comforting enough for a cozy Sunday dinner.

Preparing this dish is a true labor of love, specifically during the caramelization process, but trust us the payoff is immense. Every spoonful of this French Onion Broccoli Cheese Casserole delivers a balance of textures and flavors: the bite of the broccoli, the smooth, nutty tang of the cheese sauce, and the incredible, deep savoriness of the onion base. Get ready to ditch boring side dishes forever and welcome this irresistible fusion into your repertoire. The following guide provides everything you need to execute this recipe flawlessly, maximizing flavor and ensuring perfection from start to finish.

Why You’ll Love This Elevated Cheesy Broccoli Bake

The standard broccoli casserole holds a dear place in our hearts, reminding us of potlucks and holiday gatherings. But the French Onion Broccoli Cheese Casserole transforms that nostalgic dish into something truly gourmet. The reasons to fall head over heels for this recipe are rooted deeply in its unique flavor profile and satisfying complexity.

A Symphony of Umami and Sweetness

The foundation of any good French onion soup, and thus the backbone of this casserole, is the caramelized onion base. This lengthy process breaks down the natural sugars in the onions, concentrating their flavor into a sweet, savory, almost meaty depth pure umami magic. When this rich base is combined with a roux-based béchamel and sharp, nutty Gruyère cheese, you achieve a sauce unlike any other traditional casserole. It’s comforting, yes, but also sophisticated and complex. The slight tang of balsamic vinegar and the aromatic touch of dried thyme further enhance this profile, making every forkful of this French Onion Broccoli Cheese Casserole unforgettable.

The Perfect Texture Contrast for Ultimate Satisfaction

Texture is just as critical as flavor in a truly great casserole. This recipe excels because it provides multiple satisfying textures in one dish. The interior is gloriously creamy, thanks to the half-and-half and melted cheeses. The broccoli is intentionally par-cooked to retain a slight, tender-crisp bite, preventing the dish from becoming mushy. But the real textural genius lies in the topping. A generous layer of crushed, seasoned croutons or crispy panko mixed with extra Gruyère provides a crucial, golden-brown crunch. This crispy cap seals in the moisture while offering a delightful contrast to the smooth filling below. This textural layering guarantees that this French Onion Broccoli Cheese Casserole is satisfying on every level.

Decadent Yet Approachable Comfort Food

While the preparation includes the specific steps of making a roux and caramelizing onions, the final assembly is straightforward. This dish feels luxurious the use of rich beef broth and two high-quality cheeses (Gruyère is non-negotiable for that authentic French onion flavor) makes it feel like an indulgence. Yet, the main components are simple and accessible: butter, flour, milk, and broccoli. This perfect balance makes it an excellent choice for impressing guests without requiring advanced culinary skills. It serves beautifully as the centerpiece of a vegetarian meal or as the ultimate side dish to roasted chicken, pork tenderloin, or steak.

Moreover, if you are looking for dishes that blend creamy textures with savory depth, you might also enjoy our recipe for French Onion Pasta, which utilizes a similar flavor base for another spectacular comfort meal. This casserole brings that bistro quality right into your home kitchen.

Why You Should Try This Recipe Now for Your Next Dinner

The commitment required to caramelize onions often deters home cooks, but embracing this process is the key difference between a good casserole and a spectacular one. If you are seeking a culinary project that yields immense rewards, or simply looking to upgrade a tired side dish, now is the time to master this French Onion Broccoli Cheese Casserole.

Mastering the Art of Caramelization

This recipe provides the perfect opportunity to practice and master onion caramelization. It requires patience and low heat it cannot be rushed. Spending an hour nurturing those onions, watching them transform from harsh, white rings into sweet, brown, sticky gold, is deeply satisfying. This technique is fundamental to classic French cooking, and once you realize how easy it is (it just takes time!), you will apply it to many other dishes, including soups, dips, and even sandwiches. Do not skimp on the time for the onions; they are the heart of the French Onion Broccoli Cheese Casserole flavor profile.

An Ideal Make-Ahead or Prep-Friendly Dish

While the total time commitment looks long due to the onions, much of the casserole can be prepped ahead. The entire caramelized onion mixture can be made 1–2 days in advance and stored in the refrigerator, drastically cutting down assembly time on the day you plan to bake. You can even assemble the entire French Onion Broccoli Cheese Casserole (minus the topping) and refrigerate it overnight. This flexibility makes it an ideal dish for busy weeknights or for entertaining, allowing you to focus on the main course while the side patiently waits.

Elevating the Humble Broccoli

Broccoli is notoriously difficult to get right in a casserole it often ends up gray and waterlogged. By par-cooking the broccoli until it’s only slightly tender (al dente), we ensure it holds its bright color and texture during the baking process. When coated in this sophisticated cheese and onion sauce, even the most skeptical eaters will find themselves enjoying the vegetable. The complexity of the French onion base disguises the typical ‘vegetable’ flavor, making this an excellent way to incorporate greens into a comforting family meal.

If you’re already a fan of cheesy bakes and comfort vegetables, trying this recipe after mastering simpler classics like a Cheesy Vegetable Casserole will show you just how much a few extra minutes of preparation can elevate a dish into a truly memorable culinary experience.

Ingredients and Necessary Utensils for Perfection

Achieving the perfect French Onion Broccoli Cheese Casserole requires high-quality ingredients, particularly concerning the cheese and the broth, and the right equipment to handle the long cooking time of the onions. Here is a detailed look at what you need and why each component is essential.

Key Ingredients for the French Onion Base

The success of this casserole hinges entirely on the quality and depth of the onion base. Do not substitute these ingredients.

• 3 large yellow onions, thinly sliced: Yellow onions are preferred for their balance of flavor and sugar content, which caramelizes beautifully. Slicing them uniformly ensures even cooking.
• 4 tablespoons unsalted butter (divided) & 1 tablespoon olive oil: The fat mixture helps prevent sticking and promotes slow, even caramelization.
• 1 teaspoon dried thyme: Thyme is the classic herb for French onion soup. It adds an earthy, savory aroma.
• 1 tablespoon balsamic vinegar: This is a critical ingredient! It adds a touch of acidity and helps deepen the color and flavor of the caramelized onions, creating a robust, restaurant-quality taste.
• 1/2 teaspoon kosher salt & 1/4 teaspoon black pepper: Seasoning is vital to draw out moisture and build flavor layers.
• 1 cup rich beef broth: Use a high-quality, rich beef broth or stock. This liquid is used for deglazing and becomes part of the flavorful sauce base. Avoid using thin, watery broths; the depth of the broth directly impacts the final flavor of the French Onion Broccoli Cheese Casserole.

Ingredients for the Creamy Casserole Filling

The cheese sauce acts as the vehicle for the caramelized onions and the coating for the broccoli.

• 6 cups fresh or frozen broccoli florets: Fresh is always excellent if par-cooked correctly. If using frozen, add them straight from the freezer. We need this large quantity to ensure a good ratio of vegetable to sauce.
• 3 tablespoons unsalted butter & 3 tablespoons all-purpose flour: These form the roux the necessary thickening agent for the rich, creamy sauce. Equal parts butter and flour ensure a smooth, stable base.
• 1 1/2 cups half-and-half (or whole milk): Half-and-half provides a wonderful richness and mouthfeel. If substituting with whole milk, the sauce will be slightly thinner but still delicious. Avoid skim milk, as it compromises the creaminess essential for this French Onion Broccoli Cheese Casserole.
• 1/4 teaspoon nutmeg: A tiny pinch of nutmeg is a secret ingredient in many French and Italian white sauces (béchamel). It enhances the nutty flavor of the Gruyère and adds warmth without making the sauce taste overtly spiced.
• 1 cup shredded Gruyère cheese: This is the non-negotiable cheese for the authentic French onion flavor. Gruyère melts beautifully, has a wonderful nutty quality, and brings that signature bite associated with the soup.
• 1 cup shredded sharp white cheddar cheese: Sharp cheddar adds a necessary tang and depth that complements the sweetness of the caramelized onions. Using white cheddar helps maintain a cleaner aesthetic in the final dish.

Ingredients for the Crispy Topping

• 1 cup crushed seasoned croutons or panko breadcrumbs: Seasoned croutons offer superior flavor and texture compared to panko, but panko provides maximum crunch. Choose your favorite! Ensure the croutons are crushed into coarse crumbs.
• 1/2 cup extra shredded Gruyère cheese: This is mixed into the topping to help bind the crumbs and ensure a golden, gooey crust forms during baking.

Essential Tools and Utensils for Success

While you don’t need highly specialized equipment, the right pot for the onions is crucial.

• Large Dutch Oven or Deep Skillet: Essential for caramelizing the onions. The heavy bottom of a Dutch oven distributes heat evenly, preventing scorching during the long, low-temperature cooking required for the onions in this French Onion Broccoli Cheese Casserole.
• 9×13-inch or 3-Quart Baking Dish: The standard size for this quantity of casserole. Ensure it is adequately greased.
• Medium Saucepan: Necessary for preparing the béchamel and cheese sauce.
• Wire Whisk: Crucial for making a lump-free roux and smooth cheese sauce.
• Sharp Knife and Cutting Board: Required for the uniform, thin slicing of the onions.
• Large Bowl or Steamer Insert: Needed if you are using fresh broccoli and require par-cooking.

Having all these items measured and prepped (mise en place) before you start step one, especially the onions, will make the cooking process enjoyable and efficient. Remember, the depth of flavor in this French Onion Broccoli Cheese Casserole comes from patience and precision.

Detailed Recipe Steps for the Perfect Casserole

Follow these detailed steps carefully to ensure every element of your French Onion Broccoli Cheese Casserole is perfectly cooked, from the deepest savory onion base to the crispest golden topping.

Step 1: Caramelize the Onions (The Flavor Foundation)

This is the most critical step. Allocate ample time and resist the urge to turn up the heat.

1. Initial Sweat and Softening: Melt 2 tablespoons of butter and the olive oil in your large Dutch oven or deep skillet over medium-low heat. Add the thinly sliced onions. Cook for 20 minutes, stirring occasionally. The goal here is to release moisture and soften the onions completely, making them translucent but not yet browned.
2. Deep Caramelization: Reduce the heat to low. Continue cooking the onions for another 30–40 minutes, stirring every 5–7 minutes. The low, slow heat allows the sugars to deepen without burning. The onions must achieve a deep, rich golden-brown color and a jam-like consistency. Patience is paramount here; rushed onions will taste harsh, not sweet.
3. Seasoning and Deglazing: Once caramelized, stir in the thyme, salt, pepper, and balsamic vinegar. Cook for 1 minute to bloom the thyme.
4. Building the Base: Deglaze the pan by pouring in the 1 cup of beef broth. Bring the liquid to a simmer, vigorously scraping up any browned bits (fond) from the bottom of the pan with a wooden spoon. These bits are packed with flavor! Let the broth reduce slightly for 5 minutes, thickening slightly and concentrating the flavor.
5. Set Aside: Remove the caramelized onion mixture from the heat and set it aside. This forms the essential base for your French Onion Broccoli Cheese Casserole.

Step 2: Prepare the Broccoli and Oven

1. Preheat: Preheat your oven to 375°F (190°C). Grease a 9×13-inch or 3-quart baking dish.
2. Par-Cooking Fresh Broccoli: If using fresh broccoli, steam or boil the florets for 3–4 minutes. The goal is a bright green color and a tender-crisp texture (par-cooked). Immediately drain and rinse the broccoli with cold water to stop the cooking process. Thorough draining prevents a watery casserole. If using frozen broccoli, no pre-cooking is required; add it directly to the mixture frozen.

Step 3: Make the Rich Cheese Sauce

This is a classic béchamel adapted into a creamy cheese sauce (Mornay).

1. The Roux: In a medium saucepan, melt the remaining 3 tablespoons of butter over medium heat. Whisk in the 3 tablespoons of flour to create a smooth roux. Cook the roux for 1 minute, stirring constantly. Cooking the roux eliminates the raw flour taste.
2. Building the Béchamel: Gradually pour in the 1 1/2 cups of half-and-half (or milk), whisking continuously to prevent lumps. A slow, steady pour ensures maximum smoothness. Bring the sauce to a gentle simmer, stirring frequently, until it has thickened enough to coat the back of a spoon (about 5–7 minutes).
3. The Cheese Integration: Reduce the heat to low. Stir in the nutmeg. Remove the sauce from the heat before adding the cheese. Stir in the 1 cup of Gruyère cheese and 1 cup of sharp cheddar cheese until completely smooth and melted. Adding cheese off the heat prevents it from seizing or becoming grainy.

Step 4: Assemble the French Onion Broccoli Cheese Casserole

1. Combine Sauces: Pour the prepared cheese sauce directly into the Dutch oven containing the caramelized onion mixture. Stir until fully and evenly combined. This merging creates the rich, savory, and cheesy sauce base.
2. Fold in the Broccoli: Add the par-cooked or frozen broccoli florets to the sauce. Gently fold the ingredients together until the broccoli is evenly coated. Be careful not to break up the florets.
3. Transfer to Dish: Transfer the mixture to the prepared 9×13-inch baking dish, spreading it into an even layer.
4. Prepare the Topping: In a small bowl, combine the crushed croutons (or panko) and the extra 1/2 cup of shredded Gruyère cheese. Sprinkle this topping evenly over the casserole surface. Ensure the topping covers the entire surface for a maximum crunch.

Step 5: Bake and Rest

1. Bake Time: Bake the casserole in the preheated 375°F (190°C) oven for 25–35 minutes. The casserole is ready when the sauce is bubbling vigorously around the edges and the topping is beautifully golden brown and crisp.
2. Rest: Remove from the oven and let the French Onion Broccoli Cheese Casserole rest for 5–10 minutes before serving. This resting period allows the sauce to set slightly, preventing it from being too runny when scooped.

Tips, Variations, and Common Mistake Avoidance

This French Onion Broccoli Cheese Casserole is versatile and forgiving, provided you nail the critical step of the caramelized onions. Here are ways to customize the dish and avoid pitfalls.

Practical Tips for a Perfect Casserole

• Uniform Onion Slices: The thinner and more uniform your onion slices, the more evenly they will caramelize. Use a mandoline if you have one, or take your time with a sharp knife.
• Preventing a Grainy Sauce: Always remove the béchamel from the heat before stirring in the shredded cheese. High heat causes the dairy protein to seize and results in a grainy sauce.
• Optimal Casserole Texture: If using frozen broccoli, do not thaw it first. The baking process will cook it perfectly without making the final dish watery. If you must use fresh, stop cooking it when it still has a slight resistance to the bite.
• Maximizing the Crunch: For the crispiest topping, ensure the breadcrumbs or croutons are dry before mixing them with the Gruyère. If you are using panko, you can lightly toast them in butter before topping the casserole.

Ingredient Substitutions and Flavor Variations

While the classic components are best, you can adjust this recipe for dietary needs or flavor preferences:

• Cheese Alternatives: If Gruyère is unavailable, use Comté, Swiss (Emmentaler), or Fontina. These cheeses offer a similar nutty profile and excellent melting capability. If you need a vegetarian version of the French Onion Broccoli Cheese Casserole, ensure you use vegetable broth instead of beef broth.
• Adding Protein: Turn this side dish into a complete main course by adding cooked, shredded chicken, turkey, or ham. Stir 2 cups of cooked protein into the sauce mixture before transferring it to the baking dish.
• Vegetable Swaps: While broccoli is classic, this base works wonderfully with cauliflower, Brussels sprouts, or a mix of frozen mixed vegetables. Ensure dense vegetables, like cauliflower, are also par-cooked.
• Gluten-Free Variation: Easily make this recipe gluten-free by substituting the all-purpose flour in the roux with an equal amount of GF all-purpose blend (containing xanthan gum) or cornstarch. Use one tablespoon of cornstarch mixed with two tablespoons of cold milk before adding to the heated butter/oil mixture, then proceed as directed. Ensure you use gluten-free croutons or panko for the topping.
• Vegan Option: Achieving the depth of French onion flavor without dairy or beef broth is challenging but possible. Use mushroom broth instead of beef broth, and substitute the butter with high-quality vegan butter sticks. Replace the half-and-half with a creamy, unsweetened cashew milk or oat cream. Use a high-quality vegan cheese substitute that melts well, such as a nut-based Gruyère style block.

Storage and Make-Ahead Advice

This French Onion Broccoli Cheese Casserole is a fantastic make-ahead option.

1. Prep Ahead: Complete Steps 1 through 4 (mixing the sauce, onions, and broccoli). Spread the mixture in the baking dish but do not add the topping. Cover tightly and refrigerate for up to 24 hours.
2. Baking from Cold: If baking from cold, add an extra 10–15 minutes to the bake time. Add the topping only just before putting it into the oven to prevent the croutons from becoming soggy.
3. Freezing: You can freeze the assembled casserole (without the topping) for up to 2 months. Thaw overnight in the refrigerator before adding the topping and baking.

For more inspiration on cozy bakes and comforting casseroles, be sure to check out our collection on Pinterest: Recipes Ebook Blog Comfort Food Boards.

Nutritional Values and Health Benefits

While the French Onion Broccoli Cheese Casserole is undeniably a comfort food, it provides nutritional benefits, primarily through its star vegetable and dairy components. Understanding the nutritional breakdown can help you fit this delicious dish into your meal plan.

Approximate Nutritional Breakdown (Per Serving, based on 8 servings)

Please note that these values are estimates and can vary based on the specific type of broth, cheese, and milk used. This recipe is rich in healthy fats and protein.

• Calories: 400–450 kcal
• Protein: 18–22g
• Total Fat: 28–32g (A significant portion of this comes from the full-fat dairy and butter used in the roux and caramelized onions.)
• Saturated Fat: 16–18g
• Carbohydrates: 18–22g (Including fiber from the vegetables and starch from the flour/croutons.)
• Fiber: 4–6g

Health Benefits of Key Ingredients

The Power of Broccoli

Broccoli is a nutritional powerhouse. The large quantity used in this French Onion Broccoli Cheese Casserole provides substantial benefits, even when baked in a cheese sauce.

• Vitamin C: Broccoli is exceptionally high in Vitamin C, crucial for immune function and collagen production.
• Fiber: It is rich in dietary fiber, which aids digestion and promotes gut health.
• Antioxidants: Broccoli contains various potent antioxidants and is associated with anti-inflammatory properties.

Dairy and Nutrients

The half-and-half and, more importantly, the Gruyère and cheddar cheeses contribute essential macronutrients.

• Calcium and Vitamin D: Cheese is an excellent source of calcium, vital for bone health, and often fortified with Vitamin D.
• High-Quality Protein: The cheeses provide high-quality protein, which is necessary for muscle repair and satiety.
• B Vitamins: Dairy products contain essential B vitamins, particularly B12, important for nerve function and energy metabolism.

Onions and Flavor Depth

Caramelized onions, while mainly sugar and flavor, still contain beneficial compounds.

• Quercetin: Onions are a top source of Quercetin, a powerful flavonoid antioxidant that has been linked to reducing inflammation and fighting free radicals.
• Prebiotics: Onions contain prebiotics, which feed the beneficial bacteria in your gut, supporting overall digestive health.

This French Onion Broccoli Cheese Casserole is best enjoyed as a rich and satisfying meal. Serving it alongside a lean protein and a simple, fresh salad helps balance the richness, ensuring a complete and nutritious dinner.

FAQs about the French Onion Broccoli Cheese Casserole

Conclusion: Your New Favorite Comfort Food

The French Onion Broccoli Cheese Casserole is far more than just a recipe; it is an experience a comforting collision of classic American side dish tradition and deep, savory French culinary technique. By taking the time to slowly caramelize the onions, you unlock an incredible depth of flavor that a simple cheese sauce could never achieve alone. Paired with the nutty, melting qualities of Gruyère and the satisfying crunch of the seasoned topping, this dish is guaranteed to become a household favorite.

Whether you serve it as a lavish side dish during the holidays, a rich main course for a cozy evening, or even utilize the make-ahead features for stress-free entertaining, this casserole delivers on every promise of comfort and complexity. It’s a testament to the fact that sometimes, the simplest ingredients, prepared patiently, yield the most spectacular results.

We encourage you to set aside the time, embrace the beautiful process of caramelization, and treat yourself and your loved ones to this ultimate cheesy upgrade. We promise that once you taste the fusion of classic French onion flavor baked into a creamy, vibrant broccoli casserole, you will never look back. Don’t forget to comment below when you try the French Onion Broccoli Cheese Casserole and let us know how much you loved it!

Decadent French Onion Broccoli Cheese Casserole

A rich and savory twist on classic comfort food, this casserole combines tender broccoli and a creamy three-cheese sauce built upon a deeply flavored French onion base, topped with crispy seasoned croutons.

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Prep Time 20 minutes mins

Cook Time 1 hour hr 30 minutes mins

Total Time 1 hour hr 50 minutes mins

Servings: 8 servings

Course: Main Course, Side Dish

Cuisine: American, French

Calories: 420

Ingredients Equipment Method Notes

Ingredients

  

For the Caramelized Onions (French Onion Base)

• 3 large yellow onions thinly sliced
• 4 tablespoons unsalted butter divided
• 1 tablespoon olive oil
• 1 teaspoon dried thyme
• 1 tablespoon balsamic vinegar
• 1/2 teaspoon kosher salt
• 1/4 teaspoon black pepper
• 1 cup rich beef broth

For the Casserole Filling

• 6 cups fresh or frozen broccoli florets if frozen, do not thaw
• 3 tablespoons unsalted butter
• 3 tablespoons all-purpose flour
• 1 1/2 cups half-and-half or whole milk
• 1/4 teaspoon nutmeg
• 1 cup shredded Gruyère cheese
• 1 cup shredded sharp white cheddar cheese

For the Topping

• 1 cup crushed seasoned croutons or panko breadcrumbs
• 1/2 cup extra shredded Gruyère cheese

Equipment

• Large Dutch Oven or Deep Skillet
• 9x13-inch or 3-Quart Baking Dish
• Medium saucepan
• Whisk

Method

 

1. Caramelize the Onions

1. Melt 2 tablespoons of the butter and the olive oil in a large Dutch oven or deep skillet over medium-low heat. Add the thinly sliced onions. Cook for 20 minutes, stirring occasionally, until the onions have softened completely.
2. Reduce the heat to low. Continue cooking the onions for another 30–40 minutes, stirring every 5–7 minutes, until they are deep golden brown and heavily caramelized.
3. Stir in the thyme, salt, pepper, and balsamic vinegar. Cook for 1 minute.
4. Deglaze the pan by pouring in the 1 cup of beef broth. Bring to a simmer, scraping up any browned bits from the bottom of the pan. Let the broth reduce slightly for 5 minutes. Remove the caramelized onion mixture from the heat and set aside.

2. Prepare the Broccoli

1. Preheat your oven to 375°F (190°C). Grease a 9x13-inch or 3-quart baking dish. If using fresh broccoli, steam or boil the florets for 3–4 minutes until they are bright green and slightly tender-crisp (par-cooked). Drain thoroughly. If using frozen broccoli, you can add it directly to the casserole mixture without thawing or pre-cooking.

3. Make the Cheese Sauce

1. In a medium saucepan, melt the remaining 3 tablespoons of butter over medium heat. Whisk in the 3 tablespoons of flour to create a smooth roux. Cook for 1 minute, stirring constantly.
2. Gradually pour in the half-and-half (or milk), whisking continuously to prevent lumps. Bring the sauce to a gentle simmer, stirring frequently, until it has thickened enough to coat the back of a spoon (about 5–7 minutes).
3. Reduce the heat to low. Stir in the nutmeg. Remove the sauce from the heat and stir in the 1 cup of Gruyère cheese and 1 cup of sharp cheddar cheese until completely smooth and melted.

4. Assemble and Bake

1. Pour the prepared cheese sauce into the saucepan containing the caramelized onion mixture. Stir until fully combined.
2. Add the par-cooked or frozen broccoli florets to the sauce. Gently fold the ingredients together until the broccoli is evenly coated. Transfer the mixture to the prepared baking dish, spreading it into an even layer.
3. In a small bowl, combine the crushed croutons (or panko) and the extra 1/2 cup of shredded Gruyère cheese. Sprinkle this topping evenly over the casserole.
4. Bake the casserole in the preheated 375°F (190°C) oven for 25–35 minutes, or until the sauce is bubbly around the edges and the topping is golden brown and crisp. Remove from the oven and let the casserole rest for 5–10 minutes before serving.

Notes

For the crispiest topping, ensure your croutons are well-crushed, mimicking a coarse breadcrumb. If using fresh broccoli, make sure it is very well-drained after par-cooking to avoid a watery casserole. This dish is excellent made ahead of time (before adding the topping) and baked just before serving.