Preheat your oven to 400°F (200°C). Toss the peeled and diced butternut squash with 1 tablespoon of olive oil, salt, and pepper. Spread the pieces in a single layer on a baking sheet.
Roast for about 25-30 minutes, turning halfway through, until the squash is tender and lightly caramelized.
While the squash roasts, heat the remaining tablespoon of olive oil in a large pot or Dutch oven over medium heat.
Add the chopped onion and cook for 5-7 minutes until translucent and soft.
Stir in the minced garlic and cook for another minute until fragrant.
Add the roasted butternut squash to the pot with onions and garlic. Pour in the vegetable broth, then stir in the ground cumin and nutmeg.
Bring the mixture to a simmer and let it cook for 10 minutes, allowing the flavors to meld and the squash to soften further.
Using an immersion blender, blend the soup directly in the pot until smooth and creamy. Alternatively, carefully transfer the soup in batches to a regular blender and blend until silky.
If using coconut milk, stir it in now to add a rich, creamy texture and subtle sweetness.
Taste the soup and adjust seasoning with salt and pepper as needed.
Serve hot, garnished with a drizzle of coconut milk, toasted seeds, or fresh herbs if desired.