Before you begin, bake your pie crust and separate the egg whites from the yolks. It is important when you are making meringue that you do not have any egg yolk in the whites or it will not form.
In a medium saucepan, whisk together 1 cup sugar, flour, cornstarch, and salt.
Stir in milk, lemon juice and lemon zest.
Cook over a medium heat stirring constantly until the mixture boils. You must stir constantly or the milk will burn!
Take about a cup of the milk mixture and mix it into the egg yolks.
Then slowly pour the egg yolk mixture into the saucepan.
Continue to stir until the mixture comes to a boil and becomes thick. (This should happen at the same time- give or take)
Remove from the heat and pour into the baked pie shell. Set aside.
To make the meringue, pour egg whites into a cold mixing bowl and begin to whip. (An electric mixer works best).
Gradually add sugar and continue to whip until stiff peaks form.
Spread the meringue on top of the pie making sure you cover all the filling.
Bake for 10 minutes at 350 degrees or until the meringue is golden brown.
Remove from the oven and let cool for 30 to 45 minutes.
Cover with foil and allow pie to chill in the fridge for an additional 3 to 4 hours for best results.