Follow these simple steps to create your smooth and hearty roasted butternut squash soup:

1. Preheat the Oven: Start by preheating your oven to 400°F (200°C).
2. Prepare the Squash: Place the cubed butternut squash on a baking sheet. Drizzle with olive oil, and sprinkle with a pinch of salt and pepper. Toss to coat the squash evenly.
3. Roast the Squash: Roast the squash in the preheated oven for about 25-30 minutes, or until it is tender and lightly caramelized. Stir halfway through to ensure even roasting.
4. Cook the Aromatics: In a large pot, heat 2 tablespoons of olive oil over medium heat. Add the chopped onion and garlic, and sauté until the onion is translucent and fragrant, about 5 minutes.
5. Combine Ingredients: Add the roasted butternut squash to the pot with the onions and garlic. Pour in the vegetable broth, and stir in the ground cinnamon and nutmeg.
6. Simmer: Bring the mixture to a gentle boil, then reduce the heat to low. Cover and simmer for about 20 minutes to allow the flavors to meld together.
7. Blend the Soup: Use an immersion blender to puree the soup directly in the pot until smooth. Alternatively, transfer the soup to a blender in batches and blend until smooth, then return it to the pot.
8. Season: Taste the soup and adjust the seasoning with more salt and pepper if needed. If desired, stir in the heavy cream for a richer texture.
9. Reheat: Gently reheat the soup over low heat, stirring occasionally, until it reaches your desired serving temperature.