Make the vanillla cookie crumble:
Combine flour, baking powder, salt. Cream butter and sugar on high speed for 2 minutes, scrape sides after one minute. Add eggs on medium speed and mix until incorporated. Scrape, add vanilla extract and milk and blend on low speed just to combine. Add flour mixture and mix on low until fully incorporates. Spread on a sheet tray and bake at 325F for 10 to 15 minutes, breaking and tossing every 5 minutes. It should be golden brown. Grind 800g of the crumble into a find sand like texture. Lightly crumble the remaining 200g into pieces no smaller than a pea and reserve for later.
Melt 60g of butter and mix with the 800g of fine crumble, and press into bottom and sides of 10-inch-wide springform pan. Try to cover evenly bottom and all the way up the sides. Chill.
Make the caramelized bourbon bananas: Half and quarter bananas. Make a dry caramel in a skillet wide enough to fit the bananas in a single layer on the bottom. Once caramel is medium amber color, place bananas cut side down onto caramel and deglaze with bourbon immediately. Add butter and salt and allow to cool.
Arrange cool bourbon bananas in a single layer on the bottom of pie crust. Sprinkle about ¼ cup of the larger chunks of cookie crumble.
Make the malted pastry cream:
Bring the milk, cream, sugar, salt, vanilla and malt powder to a simmer. Mix eggs and cornstarch and temper hot dairy into the eggs. Bring everything up to a boil and boil for 2 minutes, whisking continuously. Strain and place plastic wrap on top to prevent skin from forming and cool down.
Spread malted pastry cream over bourbon banana layer until it reaches 1/3 of the way up the crust. You may have extra malted pastry cream. Sprinkle another ¼ cup of vanilla crumble and then place the pie in the fridge to firm up.
Make the roasted banana puree: Mix banana, butter, and sugar together in a roasting pan and covered with foil. Roast at 325F until the mixture takes on a purplish color. Blend, while still warm but not hot, until completely smooth.
Make the roasted banana mousse: Whip cream to medium firm peaks and fold into banana puree. Spread the banana mousse layer on top of the malted pastry cream layer leaving a half inch of space of unfilled crust above it. Again, you may have extra banana mousse. Sprinkle another ¼ cup of vanilla crumble above that. Allow that to firm up before removing the cake pan ring. To remove the cake ring warm the ring with either a blow torch or a warm wet towel. Pick up the pie by the base and place on a cake stand or large plate.
Make dulce de leech: Completely submerge the can, unopened, in a pot of cold water. Bring the water to a medium boil and continue to boil the can for an hour and a half. Do not allow the water level to get lower than the height of the top of the can or the can will explode. It will cook for about an hour. Remove and cool down completely before opening and discovery caramel milky goodness! Drizzle some on top of the roasted banana mousse.
Make some whipped cream for garnishing: Whip cream until it reaches stiff peaks and place on top of the pie however you wish, either quenelle shape like in the picture or just mound on top. Drizzle more dulce de leche on top and garnish with some fresh slices of banana if you wish. Sprinkle with some sea salt before serving.