Preheat oven to 35F.
In a bowl, combine flour, sugar, baking powder, baking soda,
and 1/8 tsp. salt.
Add buttermilk, shortening (butter or margarine) and vanilla.
Beat on low speed for 3 seconds, scraping bowl.
Beat on medium to high speed for 2 minutes, scraping bowl
Add egg whites and beat for 2 minutes more, scraping bowl.
Pour into 2 greased and floured 9 x 1/2 inch round baking
Bake for 3-35 minutes or until a toothpick comes out clean.
Cool on wire racks for 1 minutes.
Loosen sides and remove from pans.
To make a marble cake from this recipe, simply reserve one
third of the cake batter before putting in the cake pans.
Then, melt one square unsweetened or semi-sweet
chocolate either over boiling water or in the microwave oven.
Stir to blend. Add to the cake mixture and mix well.
Put one half of the chocolate batter in each cake pan in
dollops, and swirl carefully, so as not to mix the white batter
with the chocolate.
What you are trying to achieve in a marble effect.
Bake as directed.
(BTW, this is GREAT!!)