Roll dough into a 1/8-inch circle on a lightly floured surface and place in a 9-inch pie pan. Flute edge and trim 1/2 in. beyond plate rim. Chill 30 minutes. Preheat oven to 425°.
Wrap crust in double-thick foil. Use pie weights, dried beans, or uncooked rice. Bake on a lower rack until border is golden brown, 20–25 minutes. Remove foil and weights; bake 3-6 minutes longer until bottom is golden brown. Wire-rack cool. Turn down oven to 350°.
In a medium saucepan, mix sugar, cornstarch, flour, and salt. Stir in water gradually. Heat and whisk over medium heat until thickened and bubbling. Cook and stir 2 minutes on low heat. Get off the heat.
Add 1 cup heated mixture to egg yolks and return to saucepan. Bring to boil. Cook and stir 2 minutes. Get off the heat. Smoothly mix butter, lemon juice, and zest. Pour into pie crust.
Whisk egg whites and salt until stiff peaks form. Add sugar slowly until soft peaks form. Seal pie's edge to crust. Bake 12-15 minutes at 350° until meringue is golden. Cool. Put leftovers in the fridge.