1tspcoarse Kosher salt(if using table salt, use half the amount)
¾cupcold unsalted butter,diced
Filling
3large eggs
1cupgranulated sugar
3tbspall-purpose flour
3-4small lemons
Instructions
Crust and Topping
Preheat the oven to 350 F. Line an 8x8 inch baking dish with a piece of parchment paper.
In a bowl, combine the flour, sugar and salt. Scatter the cold pieces of butter over the flour mixture, and use a pastry cutter to cut the butter into the flour until moistened, crumbly, and no visible pieces of butter remain.
Measure out 1 cup of the crumb mixture, and set aside to reserve for the crumb topping.
Press the remaining crumbs firmly against the bottom of the pan. Bake for 15 minutes.
Filling
In a bowl, whisk together the eggs, sugar and flour until smooth.
Use a microplane zester to zest 3 of the lemons, and whisk the lemon zest into the eggs and sugar mixture.
Juice the lemons, measuring 1/2 cup juice. If needed, juice the 4th lemon to get a full 1/2 cup of lemon juice. Whisk the lemon juice into the egg mixture until smooth.
After the crust has baked for 15 minutes, remove from the oven, and cool for 5 minutes.
Whisk up the filling again, and carefully pour over the hot crust. Bake for 15 minutes.
Gently sprinkle the reserved 1 cup of crumbs over the filling, then continue baking for another 20 minutes, until the topping is a pale golden.
Let cool at room temperature for at least 2 hours, before slicing. These bars can be served slightly warm, or at room temperature.
Notes
Leftover bars should be stored in an airtight container, and are best eaten within 1-2 days.