Follow these detailed instructions carefully to ensure your lemon bars come out flawlessly every time. We will first prepare and pre-bake the crust, and then pour over the luscious filling to finish.

Part 1: Preparing the Shortbread Crust

1. Preheat and Prepare the Pan: Begin by preheating your oven to 350°F (175°C). Take a 9×13 inch baking pan and line it with parchment paper, leaving some overhang on the two longer sides. This overhang will act as a “sling,” making it incredibly easy to lift the entire slab of lemon bars out of the pan for clean cutting later. Lightly grease the paper and any exposed parts of the pan.
2. Combine Dry Ingredients: In a medium-sized mixing bowl, whisk together the 2 cups of all-purpose flour, ½ cup of granulated sugar, and ¼ teaspoon of salt. Whisking ensures that the sugar and salt are evenly distributed throughout the flour, which is key for a uniformly flavored crust.
3. Cut in the Cold Butter: Add the cold, cubed butter to the dry ingredients. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour mixture. Continue until the mixture resembles coarse, damp sand with some small, pea-sized butter pieces remaining. These small butter pockets will melt during baking, creating a tender, flaky texture.
4. Press the Crust into the Pan: Transfer the crumbly dough mixture into your prepared 9×13 inch pan. Use your fingers or the flat bottom of a measuring cup to press the dough down firmly and evenly across the entire bottom of the pan. Ensure you create a level, compact base.
5. Pre-Bake the Crust (Blind Baking): Place the pan in the preheated oven and bake for 20-25 minutes. You’re looking for the crust to be lightly golden brown around the edges and set in the center. This step, known as blind baking, is crucial. It ensures the crust is fully cooked and creates a barrier that prevents the lemon filling from making it soggy.

Part 2: Creating and Baking the Luscious Lemon Filling

1. Prepare the Filling While the Crust Bakes: In a large bowl, whisk together the 1 ½ cups of granulated sugar and the ¼ cup of all-purpose flour. Breaking up any lumps is important for a silky-smooth final texture.
2. Add the Wet Ingredients: To the sugar and flour mixture, add the 4 large eggs and whisk vigorously until the mixture is smooth, pale, and well-combined. Next, pour in the ⅔ cup of fresh lemon juice and the 1 tablespoon of lemon zest. Continue to whisk until everything is fully incorporated and the filling is uniform.
3. Pour and Bake: Once the crust is finished with its pre-bake, carefully remove it from the oven. Immediately and evenly pour the prepared lemon filling over the hot crust. The heat from the crust will begin to set the bottom of the filling right away.
4. Final Bake: Return the pan to the 350°F (175°C) oven. Bake for an additional 20-25 minutes. The lemon bars are done when the center is just set and no longer jiggles when the pan is gently shaken. The edges may be slightly puffed and a very light golden brown. Be careful not to overbake, as this can result in a slightly rubbery or eggy texture.
5. Cool Completely: This is one of the most important steps. Remove the pan from the oven and place it on a wire rack to cool completely to room temperature, which will take about 1-2 hours. Once at room temperature, transfer the pan to the refrigerator to chill for at least 2 more hours, or preferably overnight. Chilling is essential for the filling to firm up completely, allowing for clean, beautiful slices.
6. Cut and Serve: Once thoroughly chilled, use the parchment paper overhang to lift the entire slab of lemon bars out of the pan and onto a cutting board. Dust generously with powdered sugar just before serving. Use a large, sharp knife to cut into squares. For extra-clean cuts, wipe the knife clean between each slice.