Preparation

Make the crust:

• Line a straight-sided 13 x 9 inch metal baking pan with foil, letting the ends create an overhanging edge for easy removal. Lightly coat the sides of the foil (not the bottom) with nonstick cooking spray, oil, or melted butter to prevent the lemon topping from sticking.
• In a medium bowl, stir together the butter, sugar, and salt. Stir in the flour to make a stiff dough. Press the dough evenly into the bottom of the prepared pan. Prick the dough all over with a fork. Refrigerate the pan for 30 minutes (or freeze for 5 to 7 minutes), until the dough is firm.
  

• Meanwhile, position a rack near the center of the oven and heat the oven to 325°F.
• Bake until the crust is golden and set, about 30 minutes. Meanwhile, make the lemon topping.

Make the topping:

• In a medium bowl, whisk the eggs, sugar, flour, and salt together until smooth, about 1 minute. Whisk in the lemon juice and zest.
  

• Pour the topping over the hot crust. Return the pan to the oven and increase the heat to 350°F. Bake until the topping is set in the center (it no longer wiggles when the pan is moved) and the edges are golden, 20 to 25 minutes.
  

• Set the pan on a metal rack to cool until the crust is completely firm, at least 1 hour. (For faster cooling, put the bars in the fridge once the pan is no longer piping hot, or even outside in winter.)
• When the bottom of the pan is cool, carefully lift the bars from the pan using the foil sides and transfer them to a cutting board. Separate the foil from the bars by sliding a spatula between them. Sift the confectioners’ sugar over the lemon topping. Cut the bars into 2-inch squares.

Make Ahead Tips

The bar cookies will keep, refrigerated, for 3 to 4 days. Serve at room temperature.