Make the shell: Combine the flour, sugar, and salt, and cut in the butter and shortening until the mixture resembles coarse meal.
Add 3 tablespoons of the ice water, add the vanilla, and toss the mixture until the liquid is incorporated, adding more water if necessary.
Form the dough into a ball, flatten the ball slightly, wrap in plastic, and chill for 30 minutes.
Roll out the dough intoa 1/8 inch thick round, fit it into a 9 inch piepan, and crimp the edge decoratively.
Prick the shell lightly with a fork, line it with wax paper, and fit a smaller piepan into the shell or fill it with beans or rice to weight it down.
Bake the shell on a baking sheet in the lower third of oven at 400° F for 15 minutes.
Remove the pan and paper and bake the shell for 10 minutes more, or until it is pale golden.
Let cool in the pan on a rack.
Make the filling: In a stainless steel or enameled saucepan combine the sugar, cornstarch, lemon peel, lemon juice, and salt.
Add the yolks one at a time, beating well after each addition, and stir in the milk in a stream and the butter.
Bring to a boil, stirring, and simmer, stirring, for 2 to 3 minutes or until thickened.
Remove the pan from the heat, stir in the vanilla, and let the mixture cool for 5 minutes.
Spoon the mixture into the shell, smoothing the top, and let it cool to room temperature.
Make the meringue: In a large bowl beat the egg whites with the salt until soft peaks form, add the sugar a little at a time, and beat until stiff.
Beat in the vanilla.
Decoratively spoon or pipe the meringue over the filling, covering it completely and sealing the edges.
Lightly sift confectioner's sugar over the top and bake in a 350° F oven for 15 minutes, or until top is pale gold.