Preheat your oven to 350°F (175°C).

Combine the flour and powdered sugar in a mixing bowl.

Add the cold, cubed butter and blend until it resembles coarse crumbs.

Stir in the egg yolk, then mix in cold water until the dough comes together.

Shape the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Roll out the chilled dough to about 1/8 inch thick and cut into circles for the tartlet pans.

Line the dough in the pans with parchment paper and fill with weights. Bake for 15 minutes, then remove and bake for an additional 5-7 minutes until golden.

Whisk together the lemon juice, lemon zest, sugar, and eggs in a saucepan over medium heat.

Add the butter and cook while stirring until the mixture thickens, about 5-7 minutes.

Strain the curd through a fine-mesh sieve into a bowl.

Pour the cooled lemon curd into the cooled tart shells.

Beat the egg whites with cream of tartar until soft peaks form.

Gradually add sugar while beating until stiff peaks form.

Spread or pipe the meringue over the lemon curd.

Bake in the oven for 8-10 minutes until the meringue is golden brown.

Cool the tarts slightly before serving.

Serve chilled or at room temperature.