1Combine the first 3 ingredients in a heavy saucepan; Stir well.
2Combine the egg yolks and half and half; gradually stir into the sugar mixture.Add the chocolate. Cook over medium heat, stirring constantly, until mixture thickens and comes to a boil.Boil 3 minutes.
3Remove from heat and stir in the butter and vanilla. Immediately pour into the pie shell. Cover with plastic wrap and chill 30 minutes or until firm.
4Beat the whipping cream with a little sugar until firm peaks form. Spread over pie when it is completely cool. Dust with a little cocoa or shaved chocolate.