9 inch pie shell, cooled, or graham cracker shell
In medium saucepan, stir together cocoa, sugar, cornstarch and salt.
Gradually add milk to dry ingredients, stirring until smooth.
Cook over medium heat, stirring constantly, until mixture boils; boil l minute.
Remove from heat; stir in butter and vanilla.
Pour into baked pie crust.
Carefully press plastic wrap directly onto pie filling.
Cool; refrigerate 6 to 8 hours.
Cover; refrigerate leftover pie.