01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans and line the bottoms with parchment paper.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until evenly distributed.
03 - In a large bowl, beat the softened butter and granulated sugar with an electric mixer until light and fluffy, about 3 minutes. Add eggs one at a time, beating well after each addition. Stir in the vanilla extract.
04 - Blend the mashed bananas into the wet mixture. Alternately add the flour mixture and buttermilk in three additions, beginning and ending with the flour. Mix until just combined — do not overmix.
05 - Divide the batter evenly between the two prepared pans. Bake for 30–35 minutes, or until a toothpick inserted into the center of each layer comes out clean.
06 - Allow the cakes to cool in their pans for 10 minutes, then invert onto a wire rack to cool completely before assembling.
07 - Whisk the instant vanilla pudding mix with cold whole milk until smooth and thickened, about 2 minutes. Gently fold in the whipped heavy cream until no streaks remain.
08 - Place one cooled cake layer on a serving platter. Spread half of the pudding filling evenly over the top. Arrange sliced bananas across the surface and scatter half of the crushed vanilla wafers over the bananas.
09 - Carefully place the second cake layer on top. Spread the remaining pudding filling over it and layer with additional banana slices and the remaining crushed vanilla wafers.
10 - Beat the heavy whipping cream with powdered sugar and vanilla extract until stiff peaks form. Spread or pipe the whipped cream over the top and sides of the assembled cake.
11 - Refrigerate the cake for at least 2 hours to allow the layers to set. Garnish with additional banana slices and wafer crumbs before serving if desired.