For the Cream Cheese Frosting
Beat butter and cheese at high speed of a mixer until fluffy. Gradually add sugar and vanilla; beat at low speed just until blended (do not overbeat, or icing will become runny). Cover and chill.
For the Banana Cake
Preheat oven to 350 degrees F.
Coat bottoms of 2 9-inch round cake pans with wax paper. Coat wax paper with cooking spray. Dust with flour; set aside. In a large bowl; beat sugar and vegetable shortening at medium speed of a mixer for 5 minutes. Add eggs, one at a time, beating well after each addition. In a medium bowl, combine flour, baking soda and salt. In another small bowl, combine the mashed bananas and buttermilk (I usually save some work by placing whole banana and buttermilk in a blender). Combine flour mixture and buttermilk mixture alternatively, to creamed sugar mixture, beginning and ending with flour mixture.Pour batter into prepared cake pans. Bake at 350 degrees for 30 minutes. Let cool in pans 5 minutes on a wire rack. Loosen cake layers from sides of pans using narrow metal spatula; turn out onto wire racks. Peel off wax paper; let cool completely.
Place one cake layer on plate. Spread with 1/2 cup cream cheese icing; top with banana slices. Top with other cake layer. Frost top and sides of cake with remaining icing. Chill cake 1 hour.