1. In a large bowl, combine flour, salt and sugar. Mix well, then cut in shortening until mixture resembles coarse meal.
2. In a small bowl, combine egg, vinegar, and 4 tablespoons of water. Whisk together, then add gradually to flour mixture, stirring with a fork. Mix until dough forms a ball. Add one more tablesoon of wather if necessary.
3. Allow dough to rest in refrigerator 10 minutes before rolling out.
Preheat oven to 400F
Line shell with wax paper and fill with rice or pie weights. Bake shell in middle of oven 10 minutes. Remove paper and rice carefully and bake until golden, aboutu 12 minuutes more. Cool shell in pie plate on a rack.
LOWER OVEN TEMPERATURE TO 350F
In a heavy saucepan, whisk together sugar, cornstarch, and salt and gradually whisk in water and milk, whisking until it comes to a boil. Gradually whisk 1 cup milk mixture into yolks mixture into milk mixture. Simmer mixture, whisking, 3 minutes. Remove pan form heat and whisk in butter, lemon juice and zest until butter is melted. Cover surface of the filling with plastic wrap.
In another bowl with an electric mixer beat egg whites with cream of tartar and a pinch of salt until they hold soft peaks. Beat in sugar in a slow stream, beating until meringue just holds stiff peaks.
Pour filling into shell and spread meringue on top, covering filling completely, sealing it to pastry. Draw meringue up into peaks and bake pie in middle of oven until meringue is golden, about 15 minutes.