01 - Preheat the oven to 350°F. Grease and flour two 9-inch round cake pans, then line the bottoms with parchment paper.
02 - In a medium bowl, whisk together the all-purpose 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 pale, light, and fluffy.
04 - Add the eggs one at a time, beating thoroughly after each addition. Mix in the vanilla extract until combined.
05 - Fold the mashed bananas into the butter mixture until evenly incorporated.
06 - Alternately add the flour mixture and buttermilk to the wet ingredients, beginning and ending with the flour. Mix until just combined; do not overmix.
07 - Divide the batter evenly between the two prepared pans. Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
08 - Let the cakes cool in the pans for 10 minutes, then invert onto a wire rack to cool completely.
09 - Whisk the instant vanilla pudding mix with cold whole milk until smooth and thickened, about 2 minutes. Gently fold in the whipped cream.
10 - Place one cooled cake layer on a serving platter. Spread half of the pudding filling over the top. Arrange sliced bananas and a layer of crushed vanilla wafers over the filling.
11 - Carefully place the second cake layer on top. Spread the remaining pudding filling over it and add more sliced bananas and crushed vanilla wafers.
12 - 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 cake.
13 - Refrigerate the assembled cake for at least 2 hours to allow the layers to set. Garnish with additional banana slices and wafer crumbs before serving.