In a 2 gallon saucepot or dutch oven, melt butter over medium high heat. Add onions, celery, bell peppers, tomatoes, garlic and bay leaves. Saute 35 minutes or until vegetables are wilted. Wisk in flour, stirring constantly until a white roux is achieved. Blend crawfish tails and tomato sauce into the mixture. Cook 5 minutes stirring to prevent tomato sauce from scorching. Slowly add crawfish stock or water until a sauce like consistency is achieved. Add more stock as necessary to maintain consistency. Bring to a rolling boil then reduce to a simmer and cook 30 minutes stirring occasionally. Add sherry, green onions and parsley. Cook 5 minutes and season with salt and cayenne pepper. Serve over white rice with a few dashes of Louisiana Hot Sauce.