In a medium pot, add butter and saute onions, ginger and jalapeno pepper over medium heat until onions are tender.
Add squash and chicken broth and bring to a light boil. Reduce heat to medium-low, cover and let the mixture simmer approximately 25 to 30 minutes, or until squash is tender.
Stir in evaporated milk, half & half, sugar, salt and pepper. Simmer on low for 5 minutes, then remove from heat.
Using a stick blender, puree the mixture in the pot until smooth. If a stick blender is not available, pour the mixture into a blender until 3/4 full. Cover blender and puree the entire mixture in batches until smooth. If needed, reheat soup over very low heat, stirring constantly to prevent scorching.
Ladle soup into bowls and drop a teaspoon of sour cream into the center of each soup. If desired, draw sour cream into a swirl design on top of soup using the tip of a knife. Sprinkle 1 pinch of ground cinnamon over each bowl and serve immediately.