Mix cornstarch, milks, sugar, egg yolks and chocolate chips in saucepan. Stir constantly until cornstarch, egg yolks and chocolate are completely mixed into the milks. Cook until thick. Add butter and vanilla, continue cooking until butter is melted. Pour into pre-baked 9" pie shells. Makes 2 pies.
Pies can be topped with meringue, but we like them plain or with whipped cream.