Make/heat pie crust according to package instructions. Prick the bottom of the pie crust with a fork before baking. Remove and set aside.
Heat oven to 350 degrees.
In a medium saucepan, whisk together the sugar, flour, cornstarch, and salt.
Stir in the water, lemon juice, and lemon zest. Stir continually until the mixture comes to a boil.
Stir in the butter until it is completely melted.
Put the egg yolks in a small glass bowl and gentley tempe the yolks with 1/4 cup-1/2 cup of the sugar mixture. Whisk continually so the eggs don't cook.
Pour the yolks into the saucepan and bring everything to a low boil. Stir regularly until the mixture is thick.
Remove from the heat and pour into the precooked pie crust.