GINGERSNAP CRUST: Finely grind gingersnap cookies in a food processor (yielding 2 cups). Pour into a large mixing bowl and add melted butter, stir until well combined. Press the crumb mixture firmly into the bottom and up the sides of 9-inch pie pan. Place the crust in the freezer to get hard while you make the filling.
VANILLA CUSTARD: Combine the sugar, flour, cornstarch and salt in a saucepan. Add the milk or light cream and egg yolks, whisk together until well combined.
Heat over medium-low heat, stirring/whisking constantly, until the mixture is thick and just begins to bubble. Remove from heat and add butter and vanilla extract or vanilla bean, if using. Stir to combine. Let the mixture cool for 15-20 minutes, stirring occasionally to prevent a skin from forming on the top of the cream.
Meanwhile, slice the bananas. Spread 1/2 of the banana slices evenly across the bottom of the pie shell. Pour 1/2 of the custard over the banana slices. Repeat with remaining ingredients, being sure to cover all bananas with vanilla custard so that the bananas don't turn brown. Chill the pie in the refrigerator for several hours.
Before serving, decorate as desired. We piped on homemade whipped cream and decorated with 2 sliced bananas and a Gingersnap cookie.
Cook's Note: Save the egg whites for meringue cookies or a lemon meringue pie or your favorite angel food cake.