01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans.
02 - In a bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
03 - In a large mixing bowl, cream the butter and sugar together until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
04 - Mix in the mashed bananas. Alternate adding the flour mixture and buttermilk to the batter, beginning and ending with the flour. Stir until just combined — do not overmix.
05 - Divide the batter evenly between the two prepared cake pans. Smooth the tops with a spatula.
06 - Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out clean. Cool in the pans for 10 minutes, then transfer to wire racks to cool completely.
07 - Whisk the instant vanilla pudding mix and cold milk together in a bowl for 2 minutes. Let thicken for 5 minutes, then gently fold in the whipped cream. Chill until ready to assemble.
08 - Place one cooled cake layer on a serving platter. Spread half the pudding mixture over the top. Arrange a layer of sliced bananas and sprinkle with crushed vanilla wafers.
09 - Place the second cake layer on top. Spread the remaining pudding mixture over the surface. Decorate with whipped cream, remaining banana slices, and additional crushed wafers.
10 - Refrigerate the assembled cake for at least 2 hours before serving to allow the flavors to meld and the layers to set.