Mix the flour, sugar, cocoa and salt together. Add egg yolks, milk, butter and vanilla. Cook, stirring constantly, until thick. A wire whisk works well to stair with. May have a tendency to lump when it begins to thicken; continue stirring clockwise and counter-clockwise. Lumps will disappear. Pour into baked pie crust.
Supreme Meringue: 4 - 5 egg whites, 8 T. sugar, 1 1/2 T. cornstarch. Beat egg whites until stuff but not dry. Mix sugar and cornstarch and slowly add to egg whites. Continue beating until very stiff peaks form; put on pie; seal to crust edges. Bake at 325 degrees for approximately 10 minutes, but watch closely, until light brown.
A whipped cream topping is also excellent on this pie. It is whatever your preference is.
This is also excellent as chocolate pudding and no crust.