Preheat the oven to 350 degrees F. Spray three 8-inch cake pans with nonstick spray, line with parchment and spray again. Set aside.

In a mixing bowl, combine the cookie crumbs, sugar and melted butter. Mix to coat the crumbs so you're left with a "wet sand" consistency.

Divide the crumbs between the three pans (about 5 ounces in each). Pat firmly into place.

Bake the crusts for 7 minutes.

Turn your oven to 325 degrees F.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a stand mixer fitted with the paddle attachment, beat the butter, oil, and sugars on medium-high speed until pale and fluffy, about 3 minutes. Lower the speed to medium and add the eggs, one at a time, mixing until each is fully incorporated before adding the next (about 30 seconds). Add the vanilla.

Continue to mix for an additional 1 to 2 minutes, until the mixture is smooth.

With the mixer on low, add the dry ingredients alternating with the buttermilk mixture into the creamed mixture, starting and ending with the dry ingredients. Mix until just incorporated and remove bowl from stand mixer.

Stir/whisk the mashed banana into the mixture.

Divide the batter evenly between the pans, pouring right on top of the Nilla Wafer Crust that has been baked, using a kitchen scale for the best accuracy. (For this recipe, you’ll have about 20 ounces of batter in each of the three 8-inch pans).

Carefully smooth the batter with small offset palette knife, and bake until a toothpick or skewer comes out with a few moist crumbs on it, about 35 to 40 minutes.

Let pans cool in the pans for 15 minutes, then invert cakes onto racks, gently, peeling away parchment rounds. Let cool completely.

When the cakes are completely cooled, you can wrap each layer in plastic wrap and store in the freezer for at least an hour before assembly.

The cake layers can be made up to a week or two in advance. If you plan to make it in advance, cover each cake layer with two layers of plastic wrap. When you’re ready to frost your cake, take the cake layers out of the freezer an hour before you decorate.

In a medium size mixing bowl, mix together the cream cheese, peanut butter, and sweetened condensed milk until smooth.

Stir in the milk and the pudding mix. Refrigerate for 30 minutes.

In a chilled stainless steel bowl, beat the heavy whipping cream until stiff peaks form.

Fold the whipped cream into the pudding mixture.

Cover and refrigerate until ready to assemble the cake.

In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and peanut butter. Beat on medium-high speed until smooth, about 2 to 3 seconds.

Add the powdered sugar to the bowl and mix in, slowly at first until incorporated, then increasing the mixer speed to high. Blend in the vanilla extract, salt, and heavy whipping cream. Continue to beat on medium-high speed until very fluffy, about 3 minutes, scraping down the sides of the bowl as needed.

Continue to mix by hand using a wooden spoon to smooth out air bubbles.

Place the first cake layer, crust side down, on a cake board or cake stand. I like to spread a little bit of buttercream on the board to “glue” the cake layer in place.

Pipe a rim of peanut butter buttercream around the top edge of the cake. The rim of buttercream should be kind of high. Tip: as you’re piping it on, keep your hand lifted so the buttercream falls onto the cake. Don’t push the piping bag against the cake as you pipe. This will smash the wall we’re trying to create.

Fill the center with about half of the peanut butter banana filling. Top with sliced bananas (if serving same day, otherwise, leave the bananas out if you’re making it ahead of time and freezing).

Place the second cake layer on top of the filling and repeat these steps.

The final layer will also go crust side down on the second layer of filling.

Apply a thin layer of peanut butter buttercream around the entire cake. This is the crumb coat. Freeze the cake for about 15 minutes to set the crumble coat.

After the crumb coat is set, continue to frost the cake with remaining buttercream.