lemon meringue pie

1 cup white sugar ( I use super fine sugar)
3 Tablespoons of corn starch
2 Tablespoons all purpose flour
Pinch of salt
1 1/2 cups water
4 small lemons, zested and juiced( I use Meier lemons)
2 Tablespoons butter
4 egg yolks, beaten

In a saucepan, whisk together the sugar,cornstarch, flour, and salt. Stir in the water , lemon juice and zest. Cook over medium heat, stirring, till mixture comes to a boil. Stir in butter. Temper the eggs by whisking a little of the lemon sugar mixture into them. Then slowly whisk the eggs into the saucepan. Bring back to a boil and stir till cooked and thickened.
Remove from heat and pour into the baked pie shell. Top with meringue and bake in a 350 oven for 10 minutes. Remove, let cool before slicing