Preheat oven to 400°F (200°C). Place acorn squash halves, cut-side down, on a baking sheet lined with parchment paper. Bake for 45-60 minutes, or until tender when pierced with a fork.

Let the squash cool slightly, then scoop out the cooked flesh and set aside. Discard the skins.

While squash bakes, heat olive oil in a large pot or Dutch oven over medium heat. Add chopped onion and cook until softened, about 5 minutes.

Stir in minced garlic and cook for another minute until fragrant.

Add cooked squash flesh, vegetable broth, sage, and nutmeg to the pot. Bring to a simmer, reduce heat, and cook for 15 minutes, stirring occasionally.

Carefully transfer soup to a blender (or use an immersion blender) and blend until smooth and creamy. If using a regular blender, vent the lid.

Return soup to the pot (if using a regular blender). Stir in heavy cream or coconut milk (if using) and season with salt and pepper. Heat through gently; do not boil.

Serve hot, garnished with toasted pepitas or croutons, if desired.