Prepare a 9-inch pie crust and pre-bake according to package instructions. Allow to cool.

In a saucepan, combine milk, sugar, cornstarch, and salt. Cook over medium heat, stirring constantly until the mixture thickens and boils. Continue to cook and stir for an additional 2 minutes.

In a small bowl, slightly beat the egg yolks. Gradually stir about 1/2 cup of the hot mixture into the yolks. Then, add the yolk mixture back into the saucepan. Cook for another 2 minutes, stirring constantly.

Remove from heat and stir in the butter and vanilla extract. Let the custard cool slightly, then pour into the cooled pie crust.

Arrange the sliced bananas over the custard. Cover and refrigerate until set, about 4 hours.

When ready to serve, whip the heavy cream with powdered sugar until stiff peaks form. Spread or pipe the whipped cream over the pie.

Serve chilled. Store any leftovers in the refrigerator.