Combine sugar, cocoa, cornstarch, and salt in a heavy saucepan, stirring well.
Gradually add milk, stirring until blended.
Cook over medium heat, stirring constantly, until mixture is thickened and bubbly; boil 1 minute, stirring constantly.
Remove from heat.
Beat egg yolks until thick and lemon colored.
Gradually stir about one-fourth of hot mixture into yolks; add to remaining hot mixture, stirring constantly.
Cook over medium heat 2 minutes, stirring con-standy.
Remove from heat; stir in butter and vanilla.
Immediately pour into pastry shell.
Spread Easy Cooked Meringue over filling, sealing to edge of pastry.
Bake at 425° for 5 to 7 minutes or until golden brown.
Cool.