Combine cornstarch, sugar, salt, and milk. Cook and stir over low heat until thick.
Beat egg yolks .
Stir a small amount of hot mixture into eggs, then stir the egg and pudding mixture into saucepan and cook until thick.
Add butter and vanilla.
Pour into baked pastry shell and top with meringue.
Brown in 375 degree oven for 10 minutes or until brown.