Preheat your oven to 400°F (200°C). Toss the cubed butternut squash and chopped carrots with olive oil, salt, pepper, and cinnamon if using. Spread them in a single layer on a baking sheet and roast for about 30-35 minutes, or until tender and caramelized around the edges.
Remove the roasted vegetables from the oven and let them cool slightly until warm but manageable to handle. Transfer them to a food processor or blender.
Purée the roasted vegetables until smooth and creamy. You may need to add a splash of vegetable broth to help blend into a silky texture.
Pour the purée into a large pot and stir in the remaining vegetable broth. Bring to a gentle simmer over medium heat, stirring occasionally, until heated through.
Add salt, pepper, and more cinnamon if desired. Taste and adjust the seasoning for perfect balance.
Once the soup is hot and seasoned, ladle it into bowls and swirl a spoonful of heavy cream on top for added richness. Optional garnishes can include fresh herbs or toasted bread.