To Make Filling: In a saucepan, whisk 1 cup sugar, flour, cornstarch, and salt. Stir in water, lemon juice, and zest. Cook over medium-high until boiling; add butter. Whisk ½ cup hot mix into yolks, return to pan, cook until thick, then pour into crust
To Make 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
