Melt butter in heavy large pot over medium heat. Add onion and garlic. Saute until golden, about 10 minutes. Add pumpkin, broth, sugar, allspice and crushed red pepper. Bring to boil. Reduce heat. Cover and simmer until flavors blend, about 30 minutes. Working in batches, puree soup in blender until smooth. Return soup to pot. Bring soup to simmer, thinning with coconut milk to desired consistency. Season to taste with salt and pepper. (Can be made 1 day ahead. Cover and chill. Rewarm soup before continuing.) Ladle soup into bowls. Sprinkle with nutmeg and serve.
*Canned unsweetened coconut milk is sold at Indian, Southeast Asian and Latin American markets and at many supermarkets.