Note: The Lemon Topping needs to be added to the crust immediately while it’s still warm, so make sure the eggs are at room temperature and you have juiced (and zested) your lemons before you begin the recipe.
Preheat the oven to 350 degrees F. Line a 9×13 baking pan with parchment paper so the paper overhangs the two short sides (so it can be lifted out once cooked). Spray the sides not covered in parchment with nonstick cooking spray.
Add the crust ingredients to a food processor EXCEPT for the butter, then sprinkle the butter on top. Pulse 10 to 15 times until it resembles coarse pebbles. Alternatively, whisk the ingredients together in a bowl, then cut the butter in with two forks or a pastry cutter. Press the mixture firmly into the prepared pan to the edges, then use the bottom of a glass or measuring cup to compact it.
Bake at 350 degrees F for 20 to 24 minutes until the edges are lightly golden and the center is still pale. Meanwhile, prepare the Lemon Topping to add to the crust while it’s still warm. Remove the pan from the oven and use a fork to poke very shallow holes all over the top of the warm crust. This helps bind the crust and topping together.
Whisk the eggs in a large bowl until combined; don’t overmix. Sift in the sugar and flour. Add the salt, lemon zest, and lemon juice and gently whisk until combined. Don’t overmix, or the bars will be foamy on top. Pour the topping evenly over the warm base, then gently tap the pan on the counter to release any trapped air bubbles.
Bake the bars for 20 to 26 minutes or until the center is set and the lemon topping doesn’t stick to your finger. The topping should not jiggle when you shake the pan with an oven mitt.
Cool the bars on the counter for 2 hours, then refrigerate for at least two hours before slicing and serving. I like to freeze my bars instead (wrap the pan in plastic wrap) for the cleanest slices. The bars thaw very quickly.
Once cool, lift the bars onto a cutting board using the parchment paper overhang. Dust with powdered sugar using a sieve. Cut into squares using a hot knife (run under hot water and dry), cleaning the knife between each cut. For sweeter bars, dust with additional powdered sugar.
