Preheat oven to 350 F. Place one oven rack in the top third and another rack in the middle. Divide 200g wafers apart from the rest. Leave the remaining wafers aside for an extra topping later on. Blend the 200g of wafers in a food processor until broken to a fine crumb. Place in a large bowl and mix in the melted butter, brown sugar, and salt. Press wafer crust into a 9 inch pie plate. The crust should reach up the sides.
Place 4 whole bananas on a small baking sheet and sprinkle with more brown sugar. Place the bananas on the top rack of the oven and the pie crust in the middle rack. Bake both for 25-30 minutes, or until the edges of the crust have browned.
While the crust and the bananas cool, make the custard: In a medium saucepan, add ½ cup sugar, ¼ cup corn starch, and a pinch of salt. Whisk dry ingredients until the sugar granules have broken up the cornstarch. In a separate, medium sized bowl, whisk 4 eggs. Add 2 cups milk and lightly whisk together until combined. Set the saucepan on medium heat and slowly pour in the egg mixture into the dry ingredients while stirring. Continue to slowly whisk the custard batter over medium heat, making sure to scrape the bottom of the saucepan to prevent sticking. The custard will start to foam, evaporating water and slowly thickening. Continue to whisk until it has thickened to a pudding like consistency and the whisk leaves traces in the custard as you stir it, about 7-9 minutes. Immediately remove the custard off the heat once it has thickened.
Add the butter, vanilla, and roasted bananas. Use your whisk to mix everything and simultaneously mash the bananas into the pudding.
While the banana pudding cools, make the chocolate ganache: break apart the 4oz bar of chocolate into a small bowl. Heat up ¾ cup heavy cream in a small saucepan until it simmers, AKA, releases steam and produces small bubbles around the edges. Once simmering, pour heavy cream into the small bowl of chocolate and place a plate on top of the bowl to trap the steam in it. Let it sit for 1 minute and then whisk the cream into the chocolate, creating a silky smooth ganache. Place the plate back on top to keep it warm.
Assemble the pie: Pour the banana pudding mixture into the baked and cooled wafer crust. Smooth the surface with a rubber spatula. Pour the chocolate ganache over the pudding layer and smooth over again. Crush the remaining Nilla wafers in your hand and sprinkle on top of the chocolate ganache layer. Cover the pie with plastic wrap and let chill and set in the fridge for at least 4 hours, and up to 48 hours before serving.
Before serving, use an electric mixer on medium speed to beat the heavy cream, vanilla, and sugar into a soft whipped cream, about 5 minutes. Swoop whipped cream onto set and chilled pie. Slice and serve!