Grandma's Lemon Meringue Pie

1. Preheat the oven to 180C or 350F.

Make the Lemon Filling: 

1. In a medium saucepan, whisk together 1 cup of sugar, flour, cornstarch, and salt.
2. Stir in water, lemon juice and lemon zest and cook over medium-high heat, stirring frequently, until mixture comes to a boil, then stir in the butter.
3. Place egg yolks in a small bowl and gradually whisk in 1/2 cup of hot sugar mixture, now add this to the remaining sugar mixture in the saucepan.
4. Bring to a boil and continue to cook while stirring constantly until thick.
5. Remove from heat and pour the filling into the baked pie crust.

Make the Meringue:

1. In a large glass or metal bowl, whip egg whites until foamy.
2. Add sugar gradually, and continue to whip until stiff peaks form. 
3. Spread meringue over pie, sealing the edges at the crust.
4. Bake in preheated oven for 10 minutes, or until meringue is golden brown.