1 medium apple, unpeeled, cored and finely chopped
Preheat the oven to 375 degrees F.
Prepare a 9-inch square baking pan with nonstick pan spray.
In a large bowl, beat together the sugar, margarine, and egg whites until smooth. Stir in the buttermilk. Add the flour, baking powder, baking soda, cinnamon, and salt and mix just until the ingredients are moistened. (The batter will be stiff.) Fold in the apple.
Spread the batter in the prepared pan. Bake 25 to 30 minutes, or until a toothpick inserted in the center comes out clean. Cut into nine 3-inch squares. Serve warm or at room temperature.