In a large bowl, cream butter and sugar until light and fluffy. Beat in egg yolks and egg. Add cornmeal and flour until well blended. Beat in milk and vanilla (do not over beat). Pour into the pastry shell.
Bake at 325° for 55-65 minutes or until the filling is almost set. Cool on a wire rack.
For topping, heat 1/2 cup sugar in a small heavy saucepan over low heat without stirring until partially melted, about 5 minutes. Cook and stir with a metal spoon until syrup is completely melted and golden, about 5 minutes. Stir in the milk, butter and remaining sugar (mixture will be lumpy). Cook over medium heat, stirring until a candy thermometer reads 234° (soft-ball stage). Remove from the heat.
Pour into a small bowl without stirring. Cool, without stirring, to 190°. Beat on high speed until mixture turns light brown and creamy and a candy thermometer reads 130°-137°, about 5 minutes. Immediately spread over pie. Store in the refrigerator.