Whipped cream and walnuts for topping, optional * NOTE: the book did not specify what type of chocolate to use. Make your favorite single 8 inch pie shell. Cream butter, add sugar slowly, creaming well. Blend in melted and cooled chocolate and vanilla. Add eggs, one at a time, beating 5 minutes after each addition. With electric mixer use medium speed. Turn into cooled, baked pie shell. CHill 1 to 2 hours. Before serving top with whipped cream and walnuts, if desired.