Adapted from The Barefoot Contessa Cookbook, Smitten Kitchen, and BakeorBreak.com
For the crust: Lemon layer:
8 oz. unsalted butter, at room temperature 4 extra-large eggs at room temperature
1/2 c. granulated sugar 1 2/3 c. granulated sugar
2 c. flour Zest of four lemons
1/3 c. hazelnuts – ground, but not too finely 2/3 c. freshly squeezed lemon juice, about four lemons
1/8 teaspoon kosher salt 2/3 c. flour
Confectioners’ sugar, for dusting
Preheat the oven to 350°F and grease a 9 by 13 by 2-inch glass pan or light-colored metal pan. Grease very well, or the bars will stick.
For the crust, cream the butter and sugar until mixed well, using a hand mixer or stand mixer. Combine the flour, salt, and hazelnuts in a small bowl. Add to the butter until just mixed. Using your hands, gather the dough all together the best you can and turn onto a floured surface. Gather into a ball. Flatten the dough with floured hands and press it into the greased pan. Build a 1/2-inch edge on all sides. Chill 10 minutes.
Bake the crust for 18 to 20 minutes, until very lightly browned. Let cool on a wire rack while you mix up the lemon layer.
For the lemon layer, whisk together the eggs, sugar, lemon zest, lemon juice, and flour. Pour over the crust and bake for 20 to 25 minutes or about five minutes beyond the point where the filling is set. Let cool to room temperature. Dust with confectioners’ sugar.