1. Bake pie shell; cool. Stir together sugar, cornstarch and salt in 2 quart saucepan. Combine egg yolks and milk in 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 1-3/4 cups chocolate chips; stir until chips are melted and mixture is well blended. Pour into prepared pie shell; press plastic wrap onto filling. Cool. Refrigerate several hours or until chilled and firm. Garnish with whipped cream and remaining chocolate chips, if desired. 6 to 8 servings.