Luby's Cafeteria Chocolate Chess Pie ~ 1 1/2 cups sugar, 1/3 cup all-purpose flour , 1/3 cup butter, 2 tsp unsweetened cocoa powder, 3 extra large eggs, 1 1/4 cups evaporated milk, 1/4 cup light corn syrup, 1 ounce German sweet chocolate, melted, 2 tsp vanilla extract, 9 inch unbaked pie shell