01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, ensuring even coverage to prevent sticking.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until uniformly blended. Set aside.
03 - In a large mixing bowl, beat the softened butter and granulated sugar with an electric mixer on medium-high speed until pale, light, and fluffy—approximately 3 to 4 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in the mashed ripe bananas and vanilla extract until thoroughly combined.
05 - Gradually add the dry ingredient mixture to the wet ingredients in three additions, alternating with the buttermilk. Begin and end with the dry mixture, mixing just until each addition is incorporated. Avoid overmixing to keep the cake tender.
06 - Divide the batter evenly between the two prepared cake pans. Bake for 25 to 30 minutes, or until a toothpick inserted into the center of each layer comes out clean. Let the cakes rest in the pans for 10 minutes, then invert onto a wire rack to cool completely.
07 - While the cakes cool, whisk the instant vanilla pudding mix with cold whole milk in a bowl until thickened, about 2 minutes. In a separate bowl, whip the heavy cream with powdered sugar and vanilla extract to soft peaks. Gently fold the whipped cream into the pudding until no streaks remain.
08 - Place one cooled cake layer on a serving plate. Spread a generous, even layer of the banana pudding filling over the top. Arrange sliced bananas over the filling and sprinkle with a layer of crushed vanilla wafers.
09 - Position the second cake layer on top. Spread the remaining pudding filling over the top and sides if desired. Garnish with additional banana slices, crushed vanilla wafers, and optional whipped cream.
10 - Refrigerate the assembled cake for at least 2 hours to allow the flavors to meld and the structure to set before slicing and serving.