Preheat your oven to 400°F (200°C). Toss the pumpkin chunks with one tablespoon of olive oil and half of the chopped sage leaves, then spread them evenly on a baking sheet. Roast for about 25-30 minutes until the pumpkin is tender and slightly caramelized.
While the pumpkin roasts, heat a tablespoon of olive oil in a large pot over medium heat. Add the sliced onions and cook, stirring occasionally, until they turn golden brown and sweet-smelling—about 10-15 minutes. Stir in the remaining sage and nutmeg, cooking for another minute until fragrant.
Add the roasted pumpkin to the pot with the onions. Pour in the vegetable broth and bring the mixture to a simmer. Let it cook for 10 minutes to allow flavors to meld.
Use an immersion blender to puree the soup directly in the pot until completely smooth, or transfer carefully to a blender and blend until silky. Return to low heat if necessary.
Stir in the heavy cream to add richness and adjust seasoning with salt and pepper to taste. Warm through for a few more minutes, allowing the flavors to blend.
Ladle the hot soup into bowls, then swirl with a little extra cream on top and sprinkle roasted pumpkin seeds for crunch and visual appeal. Serve immediately while steaming and fragrant.
