1 In medium saucepan, combine sugar, flour, cornstarch and salt. In a medium bowl, beat milk and egg yolks until smooth. Gradually stir into sugar mixture. Stir constantly over medium heat until mixture thickens and comes to a full boil. Boil and stir for one minute.
2 Remove from heat and stir in chocolate, butter and vanilla. Stir until melted.
3 Pour into pie shell. Place plastic wrap over filling to prevent skin from forming and chill for several hours. Top with meringue or whipped cream and chocolate curls if so desired.