In a mixing bowl, combine the flour, sugar and salt. Mix well. Add the shortening and mix until the mixture resembles coarse crumbs. Add the water and let sit 1 minute. Either using a fork or your hands, carefully press the mixture together to form a soft ball. Wrap in plastic wrap and refrigerate at least 30 minutes. Remove the dough from the refrigerator and place it on a lightly floured surface. Roll out the dough on the floured surface into a circle about 12 inches in diameter and 1/8 of an inch thick. Gently fold the circle of dough in half and then in half again so that you can lift it without tearing it, and unfold into a 9-inch by 2-inch deep-dish pie pan. Crimp the edges and place in the oven. Bake until golden, about 15 to 20 minutes. Remove from the oven and cool completely.
In a saucepan, combine the chocolate, 1 cup sugar, cornstarch and salt. Mix well. Stir in the milk. Place the pan over medium heat and bring the mixture to a gentle boil, stirring occasionally. Cook for 3 minutes, stirring constantly. Beat the egg yolks. Add 1/2 cup of the hot mixture to the egg yolks and mix well. Add the mixture back to the saucepan and continue to cook for 2 minutes. Remove from the heat and stir in the vanilla and butter. Pour the filling into the prepared pie shell and cool completely. Cover with plastic and refrigerate until chilled. Beat the egg whites, on medium speed, until soft peaks form, about 2 minutes. Add the remaining sugar and continue to beat until stiff peaks form. Spread the meringue evenly over the pie. Place in a preheated 350 degree oven, on the top rack and bake until golden brown, about 10 minutes. Remove and cut into individual servings.