For the crust:
1 c. butter, at room temperature
1/2 c. sugar
2 c. flour
1/8 tsp. kosher salt
For the filling:
6 extra-large eggs at room temperature
3 c. granulated sugar
2 Tbs. grated lemon zest (4 to 6 lemons)
1 c. freshly squeezed lemon juice
1 c. flour
Confectioners' sugar, for dusting
Preheat the oven to 350 degrees F.
For the crust, cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment. Add flour and salt to the butter until just mixed. Press into a 9x13 inch glass pan, which has been covered in heavy-duty foil. Bake the crust for 15 to 20 minutes, until very lightly browned. Let cool on a wire rack. Leave the oven on.
For the filling, whisk together the eggs, sugar, lemon zest, lemon juice, and flour. Pour over the crust and bake for 30 to 35 minutes, until the filling is set. Let cool to room temperature.
Chill, then cut into triangles and dust with confectioners' sugar.