CAKE: 1 1/2 cups sifted flour, 1 1/3 cups sugar, 1 tablespoon baking powder, 1 teaspoon salt, 1/2 teaspoon cinnamon, 1 cup sour cream, 1/2 cup butter shortening, 3 beaten egg whites ICING: 1/4 cup butter, 2 cups sugar, 2 tablespoons evaporated milk, 2 tablespoons hot water