Step 1Melt the butter in a large stockpot over medium heat. Add the celery and onion and cook until the onion is translucent, 5 minutes. Add ginger and garlic and heat through. Add the chicken stock, squash and cinnamon stick. Bring the soup to a boil. Reduce the heat and simmer until the squash is tender, 15 to 20 minutes.
Step 2Remove and discard the cinnamon stick. Pour the soup into a blender in batches and puree until smooth (or use a hand-held blender to blend it in the soup pot). Return the soup to the saucepan. Add the brown sugar, molasses, whipping cream and salt and pepper to taste. Serve in warm bowls topped with a dollop of creme fraiche.