1. Combine the squash and stock in a saucepan and bring to a boil over high heat. Reduce the heat to medium and simmer for about 20 minutes, or until the squash is very tender. 2. Cool a bit for safetys sake, then puree the mixture in a blender. (You may prepare the recipe in advance up to this point; refrigerate in a covered container for up to 2 days.) 3. Return the puree to the saucepan and turn the heat to medium-low. Stir in the sour cream, creme fraiche, or cream, along with the butter, salt and pepper to taste, and the cayenne. Cook, stirring, until heated through (do not boil), then taste and add sugar and more seasoning, if necessary. Keep warm over low heat. 4. Serve the soup with a few cooked shrimp or mushrooms if you like, and chives. NOTES : From Jean-George Vongerichten Recipe by: Good Morning America