Preheat oven to 350 degrees and set rack in middle of oven.
Place 2 cups flour, 1/2 cup sugar and salt into a large bowl. Mix with a fork.
Add the butter, and mix just until blended. Do not use a mixer.
Press the dough evenly into bottom of an ungreased 9x13 pan. Chill the dough in the pan for about 30 minutes.
Bake pastry crust for 15-20 minutes, or until lightly browned on top.*
While the crust is baking, beat the eggs and sugar together in a large bowl.
Add the lemon juice, zest and flour to the egg mixture and mix with a whisk or hand mixer until all ingredients are incorporated. If this sits for a while, waiting for the crust to bake, make sure to mix the ingredients again to ensure the sugar doesn't settle to the bottom of the bowl before pouring over the crust!
Pour filling over hot crust and bake 35-40 minutes or until set. The center should not jiggle! Let cool completely.
Dust with powdered sugar, cut into squares or triangles.
Notes
It is important to brown the crust until golden on top. This will help the pastry to be able to support the thick layer of lemon filling!
If using salted butter, omit the salt in the pastry.
Laurie's original recipe calls for 3 cups of sugar in the filling. I cut back a little because I thought the filling was a little too sweet.
I check the center of the lemon bars with a knife. If when the knife is inserted in the center of bars it comes out clean it is done. This takes between 35-40 minutes in my oven.
If your flour is lumpy at all, sift the flour before adding to the filling.