01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium bowl, cream together softened butter and granulated sugar until light and fluffy.
03 - Incorporate all-purpose flour and salt into the butter mixture. Stir until just combined and a crumbly dough forms.
04 - Press dough evenly into the bottom of the prepared pan. Bake for 18 to 20 minutes or until lightly golden.
05 - While crust bakes, whisk together granulated sugar and flour in a large bowl. Add eggs, lemon juice, and zest if using. Whisk until smooth.
06 - Pour lemon filling over the hot crust immediately after removing it from the oven.
07 - Return pan to oven and bake for 15 to 18 minutes until filling is set but slightly jiggly in the center.
08 - Remove from oven and let cool completely in the pan. Refrigerate for at least 1 hour before cutting.
09 - Lift bars from pan using parchment overhang, cut into squares, and dust generously with powdered sugar.