Preheat waffle iron. In a medium bowl, sift together flour, baking soda, baking powder and salt; set aside.
In a large bowl, cream butter and brown sugar until light and fluffy. Beat in egg yolks. Blend in flour mixture alternately with buttermilk.
In a large glass or metal mixing bowl, beat egg whites until stiff peaks form. Fold 1/3 of the whites into the batter, then quickly fold in remaining whites until no streaks remain.
Spray waffle iron with non-stick cooking spray, or lightly brush with oil. Ladle the batter onto preheated waffle iron. Cook the waffles until golden and crisp. Serve immediately.
