Preheat your oven to 350°F (175°C).

Prepare the pie crust and blind bake it for 10 minutes.

In a saucepan, whisk together sugar, cornstarch, and salt.

Gradually add water to the dry ingredients, stirring continuously.

Bring the mixture to a boil over medium heat, stirring until thickened.

Carefully whisk a small amount of the hot mixture into the beaten egg yolks to temper them.

Pour the tempered yolks back into the saucepan and cook for 2 more minutes, stirring constantly.

Remove from heat and 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 and cream of tartar until soft peaks form, then gradually add sugar and beat until stiff peaks form.

Spread the meringue over the lemon filling, sealing the edges.

Bake for 10-15 minutes until the meringue is golden brown.