In an ovenproof casserole casserole or Dutch oven melt 1/4 cup of the butter and cook the turkey wings, carrots, onions and celery until softened, about 10 minutes, stirring occasionally. Sprinkle with the flour, salt and pepper and cook for 1 minute. Pour in the white wine and 2 quarts of water and bring to a boil. Reduce heat, cover, and simmer for 1 hour and 30 minutes. Strain the soup into a large saucepan reserving the wings. Melt 1/4 cup of the remaining butter in a frying pan and cook the chicken liver, stirring frequently. Stir the liver into the soup, along with the remaining butter. Cut the meat away from the turkey wings and add it to the soup. Float some croutons on top of the soup before serving.
