9-inch baked pastry shell or crumb crust, cooled 
   5 sections (1/2 oz. each) HERSHEY'S Unsweetened Chocolate  
Baking Bar, broken into pieces 
   3 cups milk, divided 
   1-1/3 cups sugar 
   3 tablespoons all-purpose flour 
   3 tablespoons cornstarch 
   1/2 teaspoon salt 
   3 egg yolks 
   2 tablespoons butter or margarine 
   1-1/2 teaspoons vanilla extract 
   Sweetened whipped cream(optional)
1. Prepare pastry shell; cool. 
2. Combine chocolate and 2 cups milk in medium saucepan; cook  
over medium heat, stirring constantly, just until mixture boils.  
Remove from heat. 
3. Stir together sugar, flour, cornstarch and salt in medium bowl.  
Blend remaining 1 cup milk into egg yolks; stir into sugar mixture.  
Gradually add to chocolate mixture. Cook over medium heat, stirring  
constantly with wire whisk, until mixture boils; boil and stir 1 minute.  
Remove from heat; stir in butter and vanilla. 
4. Pour into prepared pastry shell; press plastic wrap directly onto  surface. Cool; refrigerate until well chilled. Top with whipped cream, if desired  
. 8 to 10 servings.