Combine 1 1/3 cups sugar, flour, and cocoa in a deep saucepan. Beat egg yolks with milk. Slowly add to sugar mixture. Cook on medium heat until thick while stirring with a flat bottomed wooden spoon. Remove mixture from heat, and stir in the butter or margarine until melted. Pour filling into baked pie crust
To Make Meringue Topping: Whip egg whites in a glass bowl. Add remaining sugar and beat until peaks form. Spread the meringue over the chocolate filling.
Bake at 350 degrees until the peaks of the meringue are browned.