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

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

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

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

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

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