Preheat oven to 350 degrees. Spray a 9 x 13 inch baking pan with cooking spray and dust with flour, then set aside. In a mixing bowl cream together sugar and butter. Add the eggs and bananas and beat well. Add the sour milk and vanilla. In a separate bowl combine flour with baking soda, baking powder and salt. Combine the wet and the dry ingredients together and then stir in the flour-coated nuts (if adding nuts). Bake at 350 degrees for approximately 30 minutes or until toothpick inserted in center of cake comes out clean. When cooled, top with the frosting of your choice.