Best Banana Cream Pie

In a saucepan, combine the sugar, flour or cornstarch, and salt. Add milk in gradually while stirring gently. Cook over medium heat, stirring constantly, until the mixture is bubbly. Keep stirring and cook for about 2 more minutes, and then remove from the burner. Stir a small quantity of the hot mixture into the beaten egg yolks, and immediately add egg yolk mixture to the rest of the hot mixture. Return to burner and cook for 2 more minutes; constantly stirring. Remove mixture from the stove; add butter and vanilla. Stir until it has a smooth consistency. Slice bananas into cooled baked pastry shell. Top with pudding mixture. Bake at 350 °F (175°C) for 12 to 15 minutes. Chill for an hour. Serve pie garnished with a dollop of whipped cream.