Mix, in a saucepan, sugar, cornstarch and salt. Gradually stir in milk. Cook over medium heat, stirring constantly, untl mixture begins to thicken. Remove from heat.
Gradually stir half of hot mixture into the slightly beaten egg yolks. Blend this into hot mixture in saucepan, Return to heat. Stir constantly until mixture boils and thickens to desired consistency. Remove from heat. Blend in 1 tablespoons butter and vanilla; cool.
Arrange a layer of sliced bananas 1/2 -inch deep in pastry shell before pouring in cooled filling.
Top with meringue. Bake at 400F until meringue is delicately browned, 8-10 mintues. Cool at room temperature.