Preheat oven to 400 degrees. Fully blind bake your pie crust according to the package directions. Allow to cool completely before adding the filling.
To make the filling: Combine the milk, heavy cream, sugar, and salt in a medium saucepan over medium heat. Whisk until all the sugar has dissolved. Bring to a gentle simmer, whisking occasionally.
In a medium bowl, whisk the egg yolks and cornstarch together until thick and smooth.
When the milk mixture is simmering, very slowly stream in 1 cup of the simmering milk to slightly warm the egg yolk mixture. Then, in a very slow stream, whisk the egg yolk mixture into the pan.
While continuously whisking, cook until the mixture is thick and big bubbles are bursting at the surface of the pan.
Remove the pan from heat and whisk in the vanilla extract and butter.
Place a piece of plastic wrap directly on top of the warm custard to prevent a "skin" from forming on top. Allow to cool for 15 minutes.
While the pudding is cooling, slice 2 bananas and arrange slices into the cooled pie shell. Don’t be skimpy with the bananas! Then, sprinkle with cinnamon.
Spread cooled filling on top of the cinnamon bananas and a piece of plastic wrap directly on top of the pie filling. (Again, to prevent a skin from forming.)
Refrigerate for at least 4 hours and up to 1 day.
When ready to serve, top with the CocoWhip topping and slice the other two bananas and place on pie.
Slice and serve.