Melt the butter in a large stockpot, then add chopped onions and sauté until browned.
Add squash, potatoes chicken broth, vegetable stock and water.
Stir in ginger, basil, salt, black pepper, cayenne pepper and crushed red pepper.
Bring to a boil then reduce heat to medium-low and simmer for 1 hour.
After simmering, the squash and potatoes should be tender and easy to pierce with a fork. Use a soup wand, blender or food processor to puree the mixture. (If using a blender or food processor, ladle the mixture in batches to puree and then transfer the blended soup back into the stockpot).
Stir in heavy cream.
Serve warm and add a dollop of sour cream and sprinkle of paprika for garnish if desired.