Roast the squash.
Preheat the oven to 425°F.
Cut the butternut squash in half lengthwise and scoop out the seeds. Brush the cut sides with about 1 tablespoon of olive oil and season with salt and black pepper.
Place the squash cut-side down on a parchment-lined baking sheet. Roast for 35–45 minutes, or until completely tender when pierced with a fork.
Let it cool for a few minutes before scooping the flesh away from the skin.
Cook the onion and garlic.
While the squash cools, heat the remaining tablespoon of olive oil in a large pot over medium heat.
Add the diced onion with a small pinch of salt and cook for 5–7 minutes, until soft and translucent.
Add the garlic, thyme, and nutmeg and cook for another 30 seconds, just until fragrant.
Add the squash and broth.
Scoop the roasted squash into the pot and pour in the broth.
Stir everything together, bring to a gentle simmer, and cook for about 10 minutes.
Blend until smooth.
Use an immersion blender to blend the soup directly in the pot until smooth and creamy.
If you’re using a countertop blender, let the soup cool slightly first and carefully blend it in batches.
Make it creamy.
Reduce the heat to low and stir in the heavy cream.
For a slightly sweeter soup, add the maple syrup. For an extra silky finish, stir in the butter.
Taste and add more salt and black pepper as needed.
If the soup is a little thicker than you like, add another splash of broth until it reaches the consistency you want.
Warm everything through gently before serving.