Combine sugar, flour, cocoa and salt in microwave safe bowl. Stir to break up cocoa lumps.
Warm milk in microwave for 2 minutes. Add to mixture and stir with a wire whisk to blend.
Microwave on high at 2 minute intervals until thickened, stirring well in between.
Separate egg yolks from the whites. Slightly beat the yolks then blend in a few spoonfuls of the chocolate mixture to temper the yolks. Add the yolk mixture to the chocolate cream mixture and blend well. Microwave for an additional two minutes then add remaining vanilla and butter stirring until blended.
Pour into baked pie shells and top with meringue made from the egg whites. Bake in a 400 degree F. oven until slightly brown. Top with a few chocolate sprinkles to identify it as a chocolate pie.