1. Preheat oven to 350 degrees
2. To Make Lemon Filling: In a medium saucepan, whisk together 1 cup sugar, flour, cornstarch, and salt. Stir in water, lemon juice and lemon zest. Then please cook over medium-high heat and stir frequently until mixture comes to a boil. Stir in butter. Pick a small bowl and place in egg yolks and gradually whisk in 1/2 cup of hot sugar mixture. Whisk egg yolk mixture back into remaining sugar mixture. Once done, bring to a boil and continue to cook while stirring constantly until thick. Remove from heat. Pour filling into baked pastry shell.
3. To Make Meringue: Make sure to whip egg whites in a large glass or metal bowl, until foamy then gradually add sugar, whipping constantly until stiff peaks form. Spread meringue over pie, sealing the edges at the crust.