Crush the vanilla wafers by placing in a heavy-duty plastic bag. Use a rolling pin to roll over the cookies to crush them. Measure until you get 2 cups of crumbs. You can also use a food processor. Add the sugar and melted butter; stir to combine.
Press the mixture evenly into a buttered pie pan.
Place the crust in the freezer to get hard while you make the filling.
Place the dry ingredients (sugar, flour, cornstarch, salt) in a saucepan. Add the light cream and whisk together. Add the egg yolks and whisk.
Heat over low heat, stirring regularly, until the mixture is thick and just begins to bubble. Add the butter and vanilla and stir. Let the mixture cool for fifteen minutes.
Spread the banana slices evenly across the bottom of the chilled pie shell. Pour the filling over the banana slices. Chill for several hours. Garnish with additional whipped cream if desired.