1Preheat oven to 325 degrees. Grease three 9 inch round pans.
2Sift the flour, baking powder and salt. Set aside.
3Cream the butter. Add sugar gradually and beat with electric mixer until light and fluffy.
4Stir baking soda into buttermilk.
5Add dry ingredients alternately with buttermilk mixture (in fourths) to butter and sugar mixture.
6Add egg whites; mix well. Add vanilla and mix.
7Pour batter into the three pans and bake for 25-30 minutes or until toothpick comes out nearly clean. Be careful not to over bake.
8Cool in pans for 15 minutes and then turn out onto cooling racks.