Preheat the oven to 375°F (190°C). Place the pie crust into a 9-inch pie dish, prick the bottom with a fork, line with parchment paper, and add pie weights or dried beans.

Bake the crust for 12 to 15 minutes, remove the weights and parchment, then bake another 5 minutes until lightly golden. Set aside.

Whisk together sugar, cornstarch, salt, and cold water in a saucepan. Cook over medium heat, stirring constantly until thick and bubbly.

Temper the egg yolks by slowly whisking a few spoonfuls of the hot mixture into them, then return yolk mixture to the saucepan. Cook for 2 more minutes while stirring.

Remove from heat and stir in lemon juice, lemon zest, and butter. Pour the hot lemon filling into the baked pie crust.

In a clean bowl, beat egg whites until foamy. Add cream of tartar and continue beating until soft peaks form.

Gradually add sugar, one tablespoon at a time, beating until stiff, glossy peaks form.

Spread the meringue over the hot lemon filling, sealing it to the edges of the crust. Create decorative peaks with a spoon.

Bake at 350°F (175°C) for 10 to 15 minutes until the meringue is lightly golden.

Let the pie cool at room temperature for 1 hour, then refrigerate for at least 2 hours before slicing.