Chocolate Cream Pie

1 c. sugar 1/3 cup flour or cornstarch 1/4 tsp. salt 2 cups milk 3 slightly beaten egg yolks 1 1oz square unsweetened chocolate 1 Tbsp. vanilla 1 Tbsp. butter 1 9" pastry shell In sauce pan combine sugar, flour or cornstarch and salt. Gradually add milk. Using a wooden spoon or wire whip, cook and stir over medium heat unitl bubbly. Cook and stir 2 minutes. Remove from heat. Stir a moderate amount of hot mixture into yolks stirring constantly so eggs won't cook. Immediately return to hot mixture, cook 2 minutes stirring constantly. Add chopped chocolate, and stir until melted and smooth. Remove from heat. Add butter and vanilla. Pour into cooled baked pastry shell. Serve with whipped cream. (To prevent skin from forming on surface of filling, put waxed paper directly on top of hot filling while to cools.)