1. Mix together the flour, sugar and salt in medium-size bowl until well blended. Using pastry blender or 2 knives, cut the shortening into flour mixture until coarse crumbs form. Gradually add the cold water, tossing with a fork until the mixture begins to come together. With your hands, shape pastry into a ball.
2. Roll the pastry out on a lightly floured surface into 13-inch circle. Roll the pastry up on the rolling pin; unroll into 9-inch pie plate. Gently fit the pastry into the pie plate, being careful not to stretch the pastry. Roll the edge of the pastry under to form a stand-up edge; with your fingers, flute edge. Place crust in refrigerator for 30 minutes to chill.
3. To bake crust, heat oven to 425 degree F. Remove pie plate from refrigerator. Prick pastry all over with a fork. Line pastry shell with aluminum foil; fill with dried beans, rice or pie weights.
4. Bake pastry in 425 degree F oven for 15 minutes. Carefully remove the aluminum foil with the beans. Continue to bake the crust for 8 to 10 minutes or until the edge of the crust is golden brown. Let cool while preparing filling.Filling:
5. Heat chocolate and 1/2 cup milk in small, heavy saucepan over low heat, stirring constantly, until chocolate melts. Combine sugar, cornstarch and salt in large saucepan. Gradually stir in remaining 3-1/2 cups milk until completely smooth. Stir in chocolate mixture.
6. Cook the chocolate mixture over medium heat, stirring constantly, until the mixture is thickened and begins to bubble, 15 to 20 minutes; then continue to cook for another 2 to 3 minutes, stirring constantly. Remove the saucepan from the heat.
7. Using a fork, beat yolks slightly in a small bowl. Stir 1/2 cup of the hot chocolate mixture into the yolks. Stir the yolk mixture into the chocolate mixture in the saucepan; cook over low heat, stirring constantly, for 1 minute (do not overcook or the eggs will begin to set up). Stir in the vanilla.
8. Pour the filling into the cooled pastry shell. Place a sheet of plastic wrap directly on the surface of the filling. Refrigerate the pie for 3 hours or until thoroughly chilled.Cream Topping:
9. Just before serving, beat together the heavy cream, confectioners sugar and vanilla in a small bowl until stiff peaks form. Spread the topping evenly over the surface of the pie. Serve immediately or refrigerate until ready to serve.