Preheat your oven to 400°F (200°C). Spread the cubed pumpkin on a baking sheet, drizzle with olive oil, and toss to coat evenly. Roast until the pumpkin is tender and slightly caramelized, about 30-35 minutes, filling the kitchen with sweet, roasted aromas.
While the pumpkin roasts, heat a splash of olive oil in a large pot over medium heat. Add the chopped onion and cook, stirring occasionally, until translucent and fragrant, about 5 minutes. Then, stir in the minced garlic and cook for another minute, until it becomes fragrant.
Add the roasted pumpkin to the pot, along with the vegetable broth, ground cinnamon, and sage leaves. Bring the mixture to a gentle simmer and cook for about 10 minutes, allowing the flavors to meld and the sage to infuse the broth.
Remove the sage leaves (they can be chopped and returned if desired, but traditional recipes often remove them), then use an immersion blender directly in the pot or carefully transfer the soup to a blender. Puree the mixture until smooth and velvety, with no chunks remaining.
Return the blended soup to the pot, season with salt and pepper to taste, and gently heat until warmed through. The soup should be smooth, creamy, and fragrant with autumnal spices.
While the soup finishes, toast pumpkin seeds in a dry skillet over medium heat until golden and fragrant, about 3-4 minutes, shaking often to prevent burning.
Ladle the hot soup into bowls and sprinkle with the toasted pumpkin seeds for a satisfying crunch. Optionally, garnish with a few sage leaves or a drizzle of olive oil for extra flavor and presentation.
