Preheat the oven to 350°F (175°C).
Prepare the pre-made pie crust in a 9-inch pie dish and bake for 10 minutes.
In a saucepan, mix sugar, cornstarch, and salt.
Add water, stirring constantly over medium heat until thickened.
In a bowl, whisk egg yolks and gradually add the hot mixture.
Return the mixture to the saucepan and cook for an additional 2 minutes.
Stir in lemon juice, zest, and butter until smooth.
Pour the lemon filling into the baked pie crust.
In a separate bowl, beat egg whites with cream of tartar until stiff peaks form.
Spread meringue over the lemon filling, sealing the edges.
Bake for 10 minutes until meringue is golden brown.
Allow to cool before serving.