• Preheat your oven to 350°F. Line the bottom of a 9 x 13" cake pan with parchment paper and leave a little hanging over the sides to make removing the lemon bars easier.

Make the Shortbread Crust:

• In a large bowl, whisk the flour, granulated sugar, salt, egg yolks, and vanilla extract. Stir in the melted butter and use a wooden spoon to mix the dough until it comes together and is cohesive.
• Add the dough mixture to the parchment-lined pan and use your hands to press and pack it down tightly and evenly into the bottom.
• Use a fork to poke several holes in the dough. Bake the crust in the preheated oven for 18 minutes. While the crust bakes start making the lemon filling.

Make the Lemon Curd Filling:

• In a large bowl, whisk the eggs, egg yolks, granulated sugar, salt, cream of tartar, and vanilla extract.
• In a medium bowl, whisk the fresh-squeezed lemon juice and flour until smooth and the flour is dissolved.
• Melt the butter in a large pot. Add the flour and lemon juice mixture and cook over medium heat, whisking constantly until thickened.
• Carefully pour the hot lemon mixture into the bowl with the eggs, whisking the egg mixture constantly so the eggs don't scramble. Add everything back into the pot and return to the stove over medium heat. Bring the mixture to a boil, whisking constantly until thick. You'll want to cook it for about 6-8 minutes over medium heat and keep whisking the entire time. Once the mixture comes to a boil it will thicken rapidly.
• Remove from heat and strain the mixture through a sieve into a large bowl. Use a whisk to promote it going through the sieve. Use a spoon to scrape the strained curd from the opposite side of the sieve. Once you have most of it strained through, use a spoon to push as much of it as you can through the sieve.
• Pour the strained lemon curd into the warm prebaked crust and use a spatula to spread it out evenly. Bake for 12-14 minutes. Remove from the oven and let cool to room temperature. Cover the pan and refrigerate for at least 3 hours (overnight is best) before slicing and serving. Dust the tops of the lemon bars generously with powdered sugar before serving.