01 - Preheat oven to 400°F. Line a large baking sheet with parchment paper.
02 - In a large bowl, combine the cubed butternut squash, sliced carrots, chopped onion, and peeled garlic cloves. Drizzle with olive oil, then season generously with salt and freshly ground black pepper. Toss to coat thoroughly, then spread the seasoned vegetables in a single layer onto the prepared baking sheet.
03 - Roast the vegetables for 30 to 35 minutes, stirring once halfway through the cooking time, until they are golden brown and tender when pierced with a fork.
04 - Carefully transfer the roasted vegetables into a large pot. Pour in the low-sodium vegetable broth, then stir in the ground cinnamon and ground nutmeg. Bring the mixture to a gentle simmer over medium heat and continue to cook for 10 minutes to allow the flavors to meld.
05 - Remove the pot from the heat. Using an immersion blender directly in the pot, or by carefully transferring the soup in batches to a stand blender, blend the mixture until it reaches a completely smooth and creamy consistency.
06 - If desired, stir in the heavy cream or coconut milk to add richness. Taste the soup and adjust the seasoning with additional salt and freshly ground black pepper as needed.
07 - Ladle the hot roasted butternut squash soup into serving bowls. Garnish with roasted pumpkin seeds, chopped fresh parsley, or a final drizzle of cream or olive oil before serving.