In a large microwave safe dish combine squash, onions and butter. Cover and microwave on high for 4 minutes. Peel squash. Stir in broth and cook on high for another 20 to 25 minutes, or until squash is tender. Puree squash, onions and broth in a food processor or blender. Add cream, salt and pepper, and microwave on high for another 3 to 4 minutes, or until heated through. Flavor with nutmeg, cloves and cinnamon to taste.