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.