In a large, heavy pot, melt butter and saute' onions, celery, bell pepper and garlic until soft. Sitr in salt, black and cayene peppers, sugar and tomato paste. Simmer, stirring occasionally, for 20 minutes. Dissolve cornstarch in water and add with wine to mixture. Cook for 20 minutes or until mixture thickens. Add crawfish, green onions and Kitchen Bouquet. Mix well. Refrigerate overnight. Reheat slowly and serve over steamed rice. Be careful not to overcook.