Preheat your oven to 350°F (175°C).
In a mixing bowl, combine flour, sugar, and salt for the crust. Cut in the butter until the mixture resembles coarse crumbs. Add the egg yolk and cold water, mixing until the dough comes together. Press the dough into a tart pan and bake for 15 minutes. Let it cool.
For the lemon filling, combine sugar, flour, cornstarch, and salt in a saucepan. Stir in water, lemon juice, and lemon zest. Cook over medium-high heat, stirring frequently, until the mixture comes to a boil. Stir in butter. Place egg yolks in a small bowl and gradually whisk in ½ cup of the hot sugar mixture. Whisk egg yolk mixture back into the saucepan. Bring to a boil and continue to cook while stirring constantly until thick. Remove from heat. Pour filling into baked pastry shell.
For the meringue, in a large glass or metal bowl, whip egg whites until foamy. Add sugar gradually, and continue to whip until stiff peaks form. Spread meringue over pie, sealing the edges at the crust.
Bake in preheated oven for 10 minutes, or until meringue is golden brown.