01 - Preheat your oven to 400°F. Line a large baking sheet with parchment paper. In a large bowl, combine the cubed butternut squash, chopped carrots, chopped onion, and peeled garlic cloves. Drizzle with 2 tablespoons of olive oil, season generously with salt and freshly ground black pepper, and toss to ensure all vegetables are evenly coated. Spread the seasoned vegetables in a single layer on the prepared baking sheet.
02 - Roast the vegetables in the preheated oven for 30 to 35 minutes, stirring them once halfway through the cooking time, until they are tender and caramelized with a golden-brown hue.
03 - Carefully transfer the roasted vegetables into a large, sturdy pot or Dutch oven. Pour in the 4 cups of vegetable broth, then stir in the 1/2 teaspoon of ground cinnamon and 1/4 teaspoon of ground nutmeg. Bring the mixture to a gentle simmer over medium heat and allow it to cook for 10 minutes, facilitating the melding of flavors.
04 - Remove the pot from the heat. Using an immersion blender, blend the soup directly in the pot until it achieves a completely smooth, velvety consistency. If using a standard blender, carefully transfer the hot soup in batches, blend until smooth, and then return the blended soup to the pot.
05 - If desired, stir in the 1/2 cup of heavy cream or coconut milk for added richness. Taste the soup and adjust the seasoning with additional salt and freshly ground black pepper according to your preference.
06 - Ladle the hot, creamy soup into individual serving bowls. Garnish each serving with roasted pumpkin seeds, freshly chopped parsley, or a delicate swirl of cream or olive oil, if using.