1. Prepare pie crust, cool.
2. Stir together sugar, cocoa, cornstarch and salt in medium saucepan. Combine eggs and milk; gradually stir into sugar mixture, blending well. Cook over medium heat, stirring constantly with wire whisk, just until mixture comes to a boil. Remove from heat.
3. Add chocolate chips, butter and vanilla. Stir until chips and butter are melted and the mixture is smooth. Pour into prepared crust. Immediately press plastic wrap onto pie surface. Refrigerate three to four hours or until firm. Garnish with whipped topping and chocolate chips. 8 servings