Preparation - Combine flour, baking soda, baking powder, and salt; set aside. Separate egg, placing egg white in a small mixing bowl and egg yolk in a medium mxing bowl. Add sour cream, milk, mashed banana, and melted butter to egg yolk and mix well. Add dry ingredient mixture and mix well again; set aside. Beat egg white until it starts to hold a peak...do not beat until stiff. Fold beaten egg white into waffle mixture. Pour batter onto a preheated waffle maker and bake until golden brown, according to your waffle maker's directions. Serve piping hot with your favorite syrup or fruit topping for breakfast.