Stir together flour, baking powder, baking soda and salt in medium bowl.
Beat together sugar and shortening in large bowl until well combined. Beat in eggs, mashed banana and vanilla.
Beat in flour mixture. Then beat in buttermilk.
Pour batter into 2 9-inch floured round cake pans, equally.
Bake for 30-35 minutes at 350 degrees.
Cool in pans 10 minutes after removed from oven, then cool completely on wire racks.
Frost one round cake with whipped cream frosting, then layer with sliced bananas.
Place second cake on top, and frost entire cake.
Garnish top with banana slices.