For the crust, mix the dry ingredients. Grate the cold butter and toss with the dry ingredients, pinching together so that all of the flour comes in contact with butter. Mix in the buttermilk then dump onto a clean surface to knead until a ball forms. Shape into a disk and cover with plastic wrap. Place into the fridge to rest for 30 minutes.

Preheat the oven to 400 degrees.

Roll out the dough on a well-floured surface until it can easily drape over a 9-inch pie plate. Form onto the pie plate, cut and crimp as needed. Place back in the fridge for 15 minutes, or 5 in the freezer. Using a fork, score the pie dough on the bottom, place parchment paper on top of the crust and fill with dried beans or pie weights.

Bake in the preheated oven for 15 minutes then remove the pie weights and continue to cook 30 more minutes or until the crust is golden brown.

For the filling, heat the milk, heavy cream, sugar and caramel sauce together in a medium saucepan just until bubbling up the sides. In the meantime, whisk the egg yolks and corn starch together in a separate bowl. Take a few ladles of the warm milk and pour it into the egg yolk mixture while whisking. Then place the egg yolk mixture into the milk. Continue to heat the mixture, stirring consistently, until the mixture thickens and large bubbles appear. Remove from the heat and whisk in the vanilla and butter.

Pour into a medium bowl and cover with plastic wrap so that the wraps is completely touching the custard. Set aside for about 30 minutes.

To assemble, cut the bananas and place them at the bottom of the baked pie crust. Pour over the slightly cooled custard and cover with plastic wrap. Place in the fridge to set for at least 2 hours.

Whip the whipped cream until soft peaks and fold together with the caramel sauce. Smooth on top of the pie, and crumble the nilla wafers on the top.