Procedures

1. 1

   Preheat the oven to 350°F.

2. 2

   Make the crust: Cut the butter into 1/2-inch pieces. In a food processor or using a handheld pastry cutter, process all the shortbread ingredients until the mixture begins to form small pea-shaped lumps.

3. 3

   Sprinkle the dough into a rectangualr 13 x 9 x 2-inch baking pan. (The bars can also be made in a square 8- or 9-inch baking pan&em;they will be thicker and take about 15 more minutes to bake.) Using your fingers or a metal spatula, press the dough firmly and evenly onto the bottom and 1/2 inch up the sides of the pan to form a 1/2-inch layer of shortbread. Prick all over with a fork.

4. 4

   Bake the shortbread in the middle of the oven until golden, about 25 minutes. Remove it to a cooling rack. (Cover with foil to keep warm if necessary.)

5. 5

   While the curst is baking, make the filling: In a large metal bowl, whisk the eggs and sugar together until well combined and a light yellow color. Stir in the lemon juice, flour, and zest.

6. 6

   When the shortbread crust is ready and still hot, pour the lemon mixture evenly over it. Lower the oven temperature to 300°F. When it has reached the lower temperature, bake the bars in the middle of the oven until set, about 30 minutes. The top should be light brown and look a little bubbly and crusty.

7. 7

   Let the bars cool completely in the pan on a cooling rack, then cut them into 3-inch squares with a nonserrated knife.