Roast the squash:
Preheat the oven to 400°F (200°C). Toss cubed squash with 1 tablespoon of olive oil, salt, and pepper. Spread evenly on a baking sheet and roast for 25–30 minutes, or until tender and caramelized.
Sauté the aromatics:
In a large pot, heat the remaining olive oil over medium heat. Add the diced onion and garlic, sautéing until soft and fragrant.
Add roasted squash and broth:
Transfer the roasted squash into the pot. Pour in the broth and stir in the cinnamon, nutmeg, and thyme. Bring to a gentle simmer for about 10 minutes.
Blend the soup:
Use an immersion blender (or a regular blender in batches) to puree the soup until smooth and creamy.
Add cream and finish:
Stir in the heavy cream or coconut milk. Taste and adjust seasoning as needed.
Serve:
Ladle the Butternut Squash Soup into bowls and garnish with roasted pumpkin seeds, fresh herbs, or a drizzle of cream.