Preheat oven to 320 degrees F.
Mix together sugar, flour, salt, soda, shortening and butter in the bowl of a stand mixer. Mix on 2nd speed for 3 minutes. Then add whole eggs, buttermilk and vanilla to the mixture and beat again for 3 minutes on 2nd speed. In a separate bowl, beat the egg whites and sugar into a meringue state. Then gently fold the meringue into the buttermilk mixture. Pour into 4 parchment lined sheet pans or 4 (4 by 13-inch) round cake pans. Bake until a toothpick comes out clean when inserted in the center of the cake.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.