For the crust: Position an oven rack in the middle of the oven and preheat to 350 degrees F.
Set aside 6 of the chocolate wafer cookies, then put the remaining cookies in a food processor with the sugar. Pulse until finely ground with a sandy texture. Add the butter and blend until combined. Press into a 9-inch pie plate. Bake, rotating the pie plate halfway through the baking time, until firm, about 15 minutes. Transfer to a cooling rack and allow to cool while you make the pudding.
For the pudding: Put the white chocolate chips in a small bowl and the peanut butter in a medium bowl; set aside.
Heat 3 1/2 cups of the milk in a large saucepan over medium heat, stirring occasionally, until steaming, 3 to 5 minutes.
Whisk together the sugar, cornstarch and 1/2 teaspoon salt in a large bowl. Whisk in the egg yolks and remaining 1/2 cup cold milk. Whisk half of the hot milk into the egg mixture until smooth, then gradually whisk the egg and milk mixture into the remaining hot milk in the saucepan. Cook over medium heat, whisking constantly, until the mixture comes to a boil. Lower to a simmer and cook, whisking constantly, until thickened to a pudding-like consistency, 3 to 4 minutes. Turn off the heat, then transfer 3/4 cup of the pudding to the bowl with the white chocolate chips and 1 1/2 cups to the bowl with the peanut butter. Add the miniature chocolate chips to the saucepan with the remaining pudding. Whisk the puddings separately until melted and smooth. Allow to cool for 10 minutes while you prepare the cookie walls.
Cut the half banana in half. Unpeel one of the pieces and cut into 6 slices. Stack 2 slices in the center of the cookie crust. Halve the remaining slices and arrange 5 pieces around the stacked pieces cut-sides in like a flower. Arrange the 3 remaining pieces on top of the banana petals.
Carefully cut the remaining 6 chocolate wafer cookies in half. Dip 4 of the cookie halves almost all the way into the white chocolate pudding (leave just enough of each cookie exposed so you have a spot to hold onto), then arrange the cookies in a square around the bananas rounded-side up. The cookies should touch each other (the pudding will work as glue); if you need to, rearrange the bananas slightly to accommodate the cookies. Dip the remaining 8 cookie halves in the chocolate pudding. Leaving a 1-inch border around the first cookie wall, arrange the cookies rounded-side up in a circle around it, overlapping the cookies ever so slightly so they stand up straight.
Spoon half of the white chocolate pudding into the center of the pie on top of the bananas, spoon half of the peanut butter pudding into the second section of the pie and then spoon half of the chocolate pudding into the outermost section of the pie. If any cookie walls fall over during this process, simply stand the cookies back up and keep filling the pie. (Once all the pudding is in the pie, the cookie walls will stand on their own and help keep the flavors separate.) Use the back of a small spoon or an offset spatula to smooth out the pudding in the pie, then top each section with the other half of the corresponding pudding. The pudding might go slightly above the cookie walls; just smooth it, being careful to keep the different flavors separate. Alternatively, you can transfer the pudding to 3 piping bags or large resealable plastic storage bags and pipe into the pie. Put plastic wrap directly over the pie, pressing on the top slightly so the pie is mostly flat, and refrigerate until fully set, at least 4 hours and up to overnight.
For the toppings: Before serving, unwrap the pie and spoon the whipped topping over the center of the pie, leaving the chocolate pudding showing as a border. Peel and thinly slice the remaining banana piece and decorate the center of the pie with the slices. Create a ring of chopped peanuts around the banana slices, roughly over the peanut butter pudding layer. Sprinkle the mini chocolate chips over the chocolate pudding layer. Slice into 8 pieces and serve immediately.
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