Preheat oven to 350°F (175°C). Mix flour and salt, cut in butter until mixture resembles coarse crumbs. Gradually add ice water, stirring until mixture forms a ball. Roll dough to fit a 9-inch pie plate. Place crust in pie plate. Press the dough evenly into the bottom and sides of the pie plate.

Bake crust in preheated oven for 10 minutes, or until crust is lightly browned. Remove from oven and let cool.

In a medium saucepan, combine 1 cup sugar, flour, cornstarch, and salt. Gradually stir in water, lemon juice, and lemon zest. Cook over medium-high heat, stirring frequently, until mixture comes to a boil.

Stir in butter. Beat egg yolks in a small bowl and gradually stir in 1/2 cup of hot sugar mixture. Stir egg yolk mixture back into remaining sugar mixture in the saucepan. Bring to a boil and continue to cook while stirring constantly until thick. Remove from heat.

Pour filling into baked pastry shell.

In a large glass or metal bowl, whip egg whites until foamy. Gradually add sugar, continuing to beat until stiff peaks form. Beat in vanilla. Spread meringue over pie, covering the filling completely.

Bake in preheated oven for 10 minutes, or until meringue is golden brown.