Combine dry ingredients in the KitchenAid® Stand Mixer bowl. Add shortening, milk and vanilla. Attach bowl and flat beater to mixer. Turn to Speed 2 and mix about 1 minute. Stop and scrape bowl. Add egg whites. Turn to Speed 6 and beat about 1 minute, or until smooth and fluffy.
Pour batter into two greased and floured 8- or 9-inch round baking pans. Bake at 350°F for 30 to 35 minutes, or until toothpick inserted in center comes out clean. Cool 10 minutes. Remove from pans. Cool completely on wire rack. Frost if desired.