Preheaat oven 350 degr

To make the lemon filling: In a medium saucepan, whisk together 1 cup sugar, flour, cornstarch, and salt. Add water, lemon juice and lemon peel. Cook over medium heat, stirring constantly, until mixture boils. Stir in butter. Place the egg yolks in a small bowl and gradually beat in ½ cup of the hot sugar mixture. Beat egg yolk blend again with the rest of sugar blend . Bring mixture to a boil and keep to cook, stirring constantly, until thickened. Remove from heat. Cast filling into baked pastry crust.