Combine cornstarch, 2/3 cup sugar, and salt in top of a double boiler; mix well. Gradually add milk; cook over medium heat, stirring constantly, just until thickened.
Beat egg yolks until thick and lemon colored. Stir one-fourth hot mixture into yolks; add to remaining hot mixture, stirring constantly. Cook an additional 2 minutes or until thickened and bubbly. Remove from heat; stir in butter and vanilla.
Place banana slices in pastry shell. Pour filling over top.
Beat egg whites (at room temperature) until soft peaks form; gradually add 2 tablespoons sugar, and continue beating until stiff peaks form. Spread meringue over filling, sealing to edge of pastry. Bake at 350° for 5 minutes or until meringue is golden brown. Serve pie warm or chilled.