For the crust:
1/2 pound unsalted butter, at room temperature 1/2 cup granulated sugar
2 cups flour
1/8 teaspoon kosher salt
For the fullsize lemon layer:
6 extralarge eggs at room temperature
2 1/2 cups granulated sugar
2 tablespoons grated lemon zest (4 to 6 lemons) 1 cup freshly squeezed lemon juice
1 cup flour
Confectioners’ sugar, for dusting [Or] for a thinner lemon layer:
4 extralarge eggs at room temperature
1 2/3 cups granulated sugar
1 tablespoon + 1 teaspoon grated lemon zest (3 to 4 lemons) 2/3 cup freshly squeezed lemon juice
2/3 cup flour
Confectioners’ sugar, for dusting
Preheat the oven to 350°F and grease a 9 by 13 by 2inch baking sheet.
For the crust, cream the butter and sugar until light in the bowl of an electric mixer fitted with the paddle attachment. Combine the flour and salt and, with the mixer on low, add to the butter until just mixed. Dump the dough onto a wellfloured board and gather into a ball. Flatten the dough with floured hands and press it into the greased baking sheet, building up a 1/2inch edge on all sides. Chill.
Bake the crust for 15 to 20 minutes, until very lightly browned. Let cool on a wire rack. Leave the oven on.
For the lemon layer, whisk together the eggs, sugar, lemon zest, lemon juice, and flour. Pour over the crust and bake for 30 to 35 minutes (less if you are using the thinner topping), or about five minutes beyond the point where the filling is set. Let cool to room temperature.
Cut into rectangles and dust with confectioners’ sugar.