Prepare the crust and filling for Vanilla Cream Pie, blending the sugar, cornstarch, salt, milk, and egg yolks in a blender with 2 very ripe bananas until completely smooth. Transfer the mixture to a saucepan and cook as directed, until thickened, stirring in the butter and vanilla at the end. Transfer to a bowl, press a piece of plastic wrap directly on the surface of the custard, and let cool completely.
Peel and thinly slice 2 firm-ripe bananas. Place half of the bananas in the bottom of the pie crust, and spoon half of the cooled custard over the bananas. Scatter the remaining bananas over the top, and top with remaining custard. Top the pie with Whipped Cream.