In a mixing bowl, combine the all-purpose flour, powdered sugar, and salt. Cut in chilled unsalted butter until the mixture resembles coarse crumbs.

Press the crumbly mixture firmly into a cookie sheet or mold, creating even edges. Bake in your preheated oven at 350°F for about 12-15 minutes, or until lightly golden.

In a saucepan, whisk together the fresh lemon juice, granulated sugar, egg yolk, cornstarch, and lemon zest. Cook on medium heat, stirring constantly, until the mixture thickens.

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

Spoon the cooled lemon filling over the baked cookie base. Top with a generous layer of meringue, creating peaks with a spatula. Return to the oven and bake at 200°F for about 30 minutes.

Turn off the oven and leave the cookies inside to cool gradually.