Preheat oven to 350 degrees F. Prepare 2 (9-inch) round cake pans by spraying with baking spray with flour, or grease 2 pans and sprinkle with flour.
To prepare cake, place first 5 ingredients in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Add eggs and egg whites, 1 at a time, beating well after each addition. Combine flour, baking powder, salt, and baking soda; stir well with a whisk. Add flour mixture and buttermilk alternately to sugar mixture, beginning and ending with flour mixture; beat well after each addition.
Pour batter into the prepared cake pans; sharply tap pans once on counter to remove air bubbles. Bake for 20 minutes or until wooden pick inserted in center comes out clean. Cool in pans for 10 minutes on a wire rack; remove from pans. Cool completely on wire rack.
To prepare frosting, place 2 tablespoons butter and the next 4 ingredients (butter through cream cheese) in a large bowl; beat with a mixer at high speed until fluffly. Add powdered sugar, and beat at low speed junt until blended (do not overbeat). Chill 1 hour.
Place 1 cake layer on a plate; spread with 1/2 cup frosting. Top with remaining cake layer. Spread remaining frosting over top and sides of cake. Store cake loosely covered in the refrigerator.