In a mixing bowl, whisk together all-purpose flour and powdered sugar until well combined. Cut chilled, unsalted butter into small pieces and add to the flour mixture, blending until it resembles coarse crumbs. Form the mixture into a dough, wrap it in plastic wrap, and chill in the refrigerator for about 30 minutes to firm it up for easy rolling.

Preheat your oven to 350°F (175°C). On a lightly floured surface, roll out the chilled dough to about 1/4-inch thickness. Using cookie cutters, cut the dough into desired shapes and place them on a parchment-lined baking sheet. Bake for 10-12 minutes, or until the edges turn lightly golden. Remove them from the oven and let the cookies cool completely.

In a medium saucepan, combine freshly squeezed lemon juice, granulated sugar, egg yolks, cornstarch, and lemon zest. Cook over medium heat while continuously whisking until the mixture thickens, approximately 5-7 minutes. Remove from heat and let it cool to room temperature while you prepare the meringue.

In a clean mixing bowl, whip the egg whites and cream of tartar on high speed until soft peaks begin to form. Gradually add the remaining granulated sugar, one tablespoon at a time, continuing to whip until you achieve stiff, glossy peaks—this should take about 5 minutes.

Carefully spoon a generous dollop of the cooled lemon filling onto each cooled cookie, spreading it evenly on top. Then, using a piping bag or a spoon, dollop the meringue over the lemon filling, creating peaks for visual appeal.

Return the assembled cookies to the preheated oven at 350°F (175°C) and bake for an additional 5-7 minutes, or until the meringue is lightly browned. Allow the cookies to cool completely at room temperature before serving.