Cut the pumpkin in half vertically and remove the seeds and stringy pulp. Place the pumpkin halves, cut side down, on a baking sheet. Roast them in the preheated to 375°F oven for about 40-45 minutes or until the pumpkin flesh is tender and can be easily pierced with a fork. Remove from the oven and let them cool.
In a skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic. Sauté for about 5 minutes or until the onion becomes translucent and fragrant.
Once the roasted pumpkin has cooled, scoop out the flesh from the skin using a spoon. Set it aside.
Place the roasted pumpkin flesh, ground cinnamon, ground nutmeg, salt, pepper, sauteed garlic and onion, stock and cream into a blender. Blend until smooth and creamy.
Pour the pumpkin pure into a pot. Bring the mixture to a simmer, and then reduce the heat to low. Let it simmer for about 10 minutes, allowing the flavors to meld together.
Ladle the pumpkin soup into bowls. If desired, garnish with roasted pumpkin seeds, chopped fresh herbs or a drizzle of olive oil.