Chill all ingredients 30 minutes prior to making crust.
In a large mixing bowl, sift together flour and salt. Using a pastry blender, cut butter into flour until mixture resembles coarse sand. Stir in water, a tablespoon at a time, until comes together. Form dough into a ball and wrap in plastic. Chill thoroughly, up to overnight, before rolling out.
Pre-heat oven to 350 F.
On a lightly floured surface with a rolling pin, roll dough out 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. Flute the edges, if desired.
Line the crust with aluminum foil and add pie weights or dry beans. Bake in preheated oven for 10 to 15 minutes until golden brown. Remove from oven, and remove foil and pie weights. Cool in the pie pan on a wire rack until room temperature, before filling.
In a medium saucepan, whisk together 1 cup sugar, flour, cornstarch, and salt. Stir in water, lemon juice and lemon zest. Cook over medium heat, stirring frequently, until mixture comes to a boil. Stir in butter. Temper the egg yolks by placing egg yolks in a small bowl and gradually whisking in 1/2 cup of hot sugar mixture. Whisk the egg yolk mixture back into the pan while pouring it into the pan in a thin stream. Bring to a boil over medium-low heat, stirring constantly, until thick. Remove from heat. Pour filling into baked pastry shell. Set aside to cool.
Preheat oven to 350 F. In a clean large glass or metal bowl, use electric hand mixer to whip egg whites until foamy. Add sugar gradually, and continue to whip until stiff peaks form. Spread meringue over pie, making sure to spread the meringue to cover the filling and seal against the pie crust. Bake in preheated oven for 10 minutes, or until meringue is golden brown.