Cup of Yum
1. Optional Step: Gather all the granulated sugar and lemon zest into a medium sized bowl. Rub the zest and sugar between clean fingers, crumbling the zest with the sugar. Continue until zest is well mixed in with the sugar and the sugar is fragrant. 
2. Preheat the oven to 325 degrees F (165 degrees C). Line the bottom and sides of a 9×13 baking pan with parchment paper, leaving an overhang on the sides. Set aside.

Shortbread Crust

1. Mix the melted butter, 1/2 cup (64g) lemon sugar, vanilla extract, and salt together in a medium bowl with a rubber spatula. Add flour and stir until the dough is thick and well combined.
2. Press shortbread dough firmly onto the parchment in your baking pan, making sure the layer is flat and even. Bake for 20 minutes or until the edges are lightly browned.

Lemon Curd Filling

1. Whisk the 2 cups (256g) lemon sugar and 1/3 cup (43g) flour together in a large bowl. Whisk in the eggs, vanilla, and lemon juice and mix until thoroughly combined.
2. Pour lemon curd filling over the crust. Bake the bars for 22-25 minutes or until the center is set and no longer jiggles. 
3. Remove pan from the oven and cool completely until room temperature in pan, about 3 hours. Cover with plastic wrap (don't let it touch the lemon curd) and let cool in the refrigerator for 2-3 hours, until completely chilled.
4. Once chilled, lift the bars out of the pan using the hanging parchment paper to cut with a large knife. To make clean squares, wipe the knife with a clean damp towel between each cut. Dust with powdered sugar and cut into squares before serving. 
5. Store leftover lemon bars in an airtight container in the refrigerator for up to 1 week.