Preheat your oven to 400°F (200°C). Place the halved pumpkin cut side up on a baking sheet, drizzling the flesh with a tablespoon of olive oil. Roast until tender and the edges are slightly caramelized, about 40 minutes.
Allow the roasted pumpkin to cool slightly, then scoop out the flesh into a bowl, discarding the skin. Set aside.
Heat a large pot over medium heat. Add a tablespoon of olive oil, then sauté the chopped onion until it becomes translucent and fragrant, about 5 minutes.
Add the minced garlic to the onions and cook for another minute until the garlic is fragrant.
Puree the roasted pumpkin flesh until smooth, then add it to the pot with the sautéed onions and garlic.
Pour in the vegetable broth, stirring well to combine. Bring the mixture to a gentle simmer over medium heat.
Season the soup with cinnamon, salt, and pepper. Let it simmer uncovered for about 10 minutes to allow flavors to meld.
Use an immersion blender to blend the soup directly in the pot until it reaches a smooth, velvety consistency. Alternatively, carefully transfer the mixture to a blender and puree until smooth, then return to the pot.
Taste and adjust seasoning with additional salt and pepper if needed. Heat through for a few more minutes if necessary.
Pour the hot soup into bowls, garnish with a drizzle of cream or a sprinkle of roasted pumpkin seeds if desired, and serve warm.
