Preheat your oven to 400°F (200°C). Place the pumpkin halves cut side up on a baking sheet and brush with olive oil. Roast until the flesh is soft and caramelized, about 40 minutes.
Allow the roasted pumpkin to cool slightly, then scoop out the flesh into a large pot. Set aside.
Into a large pot, heat a tablespoon of olive oil over medium heat. Add the chopped onion and sauté until translucent and fragrant, about 5 minutes.
Add the minced garlic, chopped sage, and ground allspice, cooking for another minute until fragrant.
Pour in the vegetable broth and bring the mixture to a gentle simmer.
Add the scooped pumpkin flesh to the simmering broth, stirring to combine. Let it cook together for about 10 minutes to meld flavors.
Use an immersion blender or transfer the mixture to a blender, then blend until smooth and creamy, achieving a velvety texture.
Return the blended soup to the heat, stir in the cream if using, and season with salt and pepper to taste. Warm through for a few minutes.
Serve the hot pumpkin soup garnished with fresh sage or a swirl of cream, enjoying its rich color and smooth consistency.
