In a medium bowl, whisk yolks; set aside.
In saucepan, combine sugar, cornstarch, salt and milk.
Cook over medium heat until mixture comes to a rolling boil for one minute.
Remove from heat; temper eggs with 1 cup of the hot mixture.
Pour egg mixture back into saucepan; boil 1 minute.
Remove from heat; stir in butter and vanilla. Set aside to cool slightly.
Slice 2 bananas into bottom of pie shell, and then add half of the cream mixture.
Slice remaining 2 bananas; place on top of cream mixture.
Pour remaining cream mixture over bananas; top with whipped cream.