Preheat your oven to 350°F (175°C). Bake the pre-made pie crust according to package instructions until golden brown.

In a saucepan, whisk together the sugar, cornstarch, and salt. Slowly add the water while stirring to combine, then cook over medium heat until thick and bubbling.

In a small bowl, beat the egg yolks. Gradually whisk in a small amount of the hot mixture to temper them, preventing curdling. Then stir the yolk mixture back into the saucepan.

Remove the saucepan from heat and stir in the lemon juice, lemon zest, and butter until fully combined.

Pour the lemon filling into the baked pie crust, spreading it evenly. Allow it to cool slightly while you prepare the meringue.

In a clean bowl, beat the egg whites and cream of tartar until soft peaks form. Gradually add sugar and continue beating until stiff peaks form.

Carefully spread the meringue over the lemon filling, ensuring it touches the crust to prevent shrinking. Create peaks with a spatula.

Bake the pie in the preheated oven for 10-12 minutes, or until the meringue is lightly browned.