Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper for easy cleanup.
Peel the pumpkin, remove the seeds, and cut it into roughly 1-inch chunks. Spread them evenly on the prepared baking sheet.
Toss the pumpkin chunks with olive oil until lightly coated. Arrange the pieces in a single layer for even roasting.
Roast the pumpkin in the oven for about 35-40 minutes, or until the edges are golden brown and caramelized, and the pumpkin feels tender when pierced with a fork.
Remove the pumpkin from the oven and allow it to cool slightly, just enough to handle comfortably.
Add the roasted pumpkin to a blender or use an immersion blender directly in the pot. Pour in the vegetable broth, then blend until smooth and creamy.
Pour the blended soup into a pot if using a blender, and bring it to a gentle simmer over medium heat. Season with salt, pepper, and cinnamon if using.
Let the soup simmer for 5-10 minutes to allow the flavors to meld and the soup to thicken slightly. Stir occasionally.
Taste and adjust seasoning as needed, adding more salt or spices to enhance the flavor.
Serve the soup hot, garnished with a drizzle of olive oil or a sprinkle of fresh herbs if desired. Enjoy its warm, velvety texture and cozy flavor.