First, make the Vanilla Wafer Crust: Preheat the oven to 325 degrees. Using the food processor, grind the cookies into fine crumbs. Add the butter and pulse until well combined. Press this up the sides and on the bottom of a 9 inch round pie pan. Bake for 15 minutes. Cool completely on a wire rack while you make your filling.
Next, make the Vanilla Cream: In a three quart saucepan whisk together the sugar, cornstarch, and salt. Slowly whisk in the milk. Then, whisk in the eggs. Whisking constantly, cook over low heat, until the mixture comes to a simmer. Cook for one minute. Remove it from the heat and add the butter and vanilla. Set aside to cool. I wait to add the bananas right before serving.
When the crust and the filling are at rooom temperature, pour the filling into the crust. Cover and chill for six hours or overnight.
Right before serving, push the once up of sliced bananas into the filling. Then, in an electric mixer, beat the heavy cream, vanilla and sugar together, until it's whipped into stiff peaks.
Put the whipped cream in a pastry bag with a star tip and pipe it around the pie edges. Add another 1 cup of sliced banana to the top of the pie.