In a saucepan cook the onion in margarine until tender. Stir in the flour, 1/4 teaspoon of salt, dash of pepper. Add the milk all at once. Cook and stir until thickened and bubbly. Stir about 1 cup of  the hot mixture into the sour cream, return all to the saucepan. Gently stir in the tuna and wine or milk. Heat through. DO NOT BOIL. Serve over muffin halves, noodles or rice. Serves 4