In a medium saucepan, whisk together 1 cup of sugar, flour, cornstarch, and salt. Stir in water, lemon juice, and lemon zest.
Cook over medium-high heat, stirring frequently, until the mixture comes to a boil. Stir in the butter.
In a small bowl, place the egg yolks and gradually whisk in 1/2 cup of the hot sugar mixture.
Whisk the egg yolk mixture back into the remaining sugar mixture in the saucepan. Bring to a boil and continue to cook, stirring constantly, until thickened. Remove from heat.
Pour the filling into the baked pastry shell.
To Make Meringue:
In a large glass or metal bowl, whip the egg whites until foamy.
Gradually add 6 tablespoons of sugar and continue to whip until stiff peaks form.
Spread the meringue over the pie, sealing the edges at the crust.
Bake:
Bake in the preheated oven for 10 minutes, or until the meringue is golden brown.