Preheat the oven to 400°F (200°C). Cut the pumpkin in half and scoop out the seeds and stringy bits.
Brush the cut sides with olive oil and sprinkle with a little salt if desired. Place the pumpkin halves cut-side down on a lined baking sheet.
Roast in the oven for 45 minutes, until the pumpkin skin is caramelized and the flesh is very tender when pierced with a fork.
Remove the pumpkin from the oven and let it cool slightly. Use a spoon to peel away the charred skin, revealing the sweet, roasted flesh.
Chop the roasted pumpkin into chunks and transfer to a blender or food processor.
Add the vegetable broth to the blender and blend until smooth and velvety, about 30 seconds.
Pour the blended mixture into a large pot and gently heat over medium heat. Stir in the heavy cream and warming spices.
Season the soup with salt and pepper to taste, adjusting the flavor as needed.
Simmer the soup for another 5–10 minutes, allowing the flavors to meld and the soup to thicken slightly.
Serve the hot soup in bowls, garnished with a swirl of cream or a sprinkle of roasted seeds if desired.
