Heat a large pot over medium heat and sauté onion and garlic until fragrant and translucent.
Stir in diced pumpkin, cinnamon, nutmeg, and cayenne pepper to coat evenly.
Pour in the vegetable broth. Bring to a simmer and cook for 20 minutes or until the pumpkin is tender.
Use an immersion blender to puree the soup until smooth. Alternatively, carefully blend in batches in a countertop blender.
Taste and add salt and black pepper as needed. Adjust spices if desired.
Ladle into bowls, garnish with sour cream or extra spices, and serve hot.
