1. Remove wrappers from chocolate bars; break into pieces and set aside. Stir together sugar, cornstarch, cocoa and salt in 2-quart saucepan. Combine egg yolks and milk in bowl or container with pouring spout. Gradually blend milk mixture into sugar mixture.
2. Cook over medium heat, stirring constantly, until mixture comes to a boil. Boil and stir 1 minute. Remove from heat; stir in butter and vanilla. Add chocolate bar pieces; stir until melted and mixture is well blended. Pour into crumb crust; press plastic wrap onto filling. Cool. Refrigerate several hours or until chilled and firm. Remove plastic wrap and garnish with whipped cream and chocolate bar sections, if desired. Cover; refrigerate leftovers. 6 to 8 servings.