Pre-bake the pie crust according to package instructions until golden brown.
In a saucepan, combine sugar, cornstarch, and salt.
Gradually whisk in the milk until smooth.
Cook over medium heat, stirring constantly, until the mixture thickens.
In a separate bowl, lightly beat the egg yolks.
Slowly add a bit of the hot mixture to the yolks to temper them.
Pour the yolk mixture back into the saucepan and stir well.
Continue cooking for a couple more minutes until thickened.
Remove from heat, then stir in butter and vanilla extract.
Pour the custard into the baked pie crust and layer the sliced bananas on top.
Cover with plastic wrap and chill in the refrigerator for at least 3 hours.
Serve with whipped cream on top and enjoy!