In a large pot, melt the butter over moderate heat. Once the butter is just beginning to brown, add the onion and sauté for 5 minutes. Add the garlic, jalapeño, chile powder, cumin and cinnamon and cook for 3 minutes. Add the pumpkin puree and broth, stirring to incorporate, then season with the salt, and bring to a boil. Reduce the heat to low and simmer for 20 minutes. Stir in the cream and let cool for 10 minutes.
Transfer the soup to a blender (or use an immersion blender in the pot) and puree until smooth. If needed, add additional water or broth to reach the desired consistency. Return the mixture to the saucepan. Serve warm and garnish with the pumpkin seeds, queso fresco and cilantro.
Like most soups, this one is even better made the day before. Reheat before serving.