Instructions

• Preheat the oven to 350°F (175°C). Lightly spray a 9" x 13" glass or ceramic baking pan with cooking spray OR line the pan with parchment paper leaving an overhang on the long sides (this overhang will help lift the bars out for cutting). Set the prepared pan aside.
• (Optional) If you want a powdered-sugar dusting on the finished bars, set aside a small amount of the 1 cup powdered sugar before you mix the crust. Do not add any extra ingredients beyond the list.
• Make the crust: in a medium bowl, combine 1 cup softened (not melted) unsalted butter, 2 cups all-purpose flour, 1 cup powdered sugar, and 1/8 teaspoon kosher salt. Mix with a large spoon, a pastry cutter, or your fingers until well combined and a dough forms.
• Press the crust mixture evenly into the bottom of the prepared 9" x 13" pan, smoothing the top so it is level.
• Bake the crust on the middle rack for 15 to 20 minutes, or until the crust is set and just beginning to turn color. Remove the pan from the oven and leave the oven on.
• While the crust is baking (or immediately after removing it), make the filling: in a mixing bowl, use an electric mixer on medium speed to beat together 6 large eggs, 3 cups granulated sugar, 4 tablespoons grated lemon zest, 1/2 cup fresh lemon juice, and 1 cup all-purpose flour. Beat until the mixture is smooth and well combined.
• Pour the filling evenly over the warm baked crust.
• Return the pan to the oven and bake for 30 to 35 minutes, or until the center is set and no longer jiggly when gently shaken; the top should be lightly golden brown. If your oven runs cool, you may need the full 35 minutes.
• Remove the pan from the oven and let the bars cool completely at room temperature (about 2 hours).
• After cooling at room temperature, chill the pan in the refrigerator for 1 to 2 hours to help the filling fully set and make cutting easier.
• To serve: if you lined the pan with parchment, use the parchment overhang to lift the bars from the pan and place them on a cutting board. If not, cut directly in the pan. Use a long non-serrated knife and wipe the blade clean between each cut for neat squares.
• If you reserved powdered sugar in step 2, dust the chilled bars with that powdered sugar before serving.