Step 1: Preheat your oven to 400°F (200°C). On a large baking sheet, toss the cubed butternut squash with 1 tablespoon of olive oil, salt, and pepper. Spread in a single layer.
Step 2: Roast the squash for 20-25 minutes, or until fork-tender and lightly caramelized. Remove from oven and set aside.
Step 3: In a large pot or Dutch oven, heat the remaining 1 tablespoon of olive oil over medium heat. Add the chopped onion and sauté for 5-7 minutes, until softened and translucent.
Step 4: Add the minced garlic to the pot and cook for another minute until fragrant, being careful not to burn it.
Step 5: Stir in the roasted butternut squash and vegetable broth. Bring to a simmer, then reduce heat and let it gently cook for 5-10 minutes to allow flavors to meld.
Step 6: Carefully blend the soup until smooth using an immersion blender directly in the pot, or transfer in batches to a standing blender. (If using a standing blender, be cautious with hot liquids and do not overfill.)
Step 7: Return the smooth soup to the pot if using a standing blender. Stir in the coconut milk or heavy cream, ground nutmeg, and cayenne pepper (if using). Heat through gently, but do not boil.
Step 8: Taste and adjust seasoning with additional salt and pepper as needed. Serve hot, garnished with your favorite toppings.