Preheat oven to 350 degrees.

CRUST:

2 c. sifted all-purpose flour
1/2 c. sifted powdered sugar
1 c. (2 sticks) butter, cut into pieces

Combine the flour with the powdered sugar in a food processor bowl. Add the butter and pulse to mix thoroughly. Pat dough evenly into the bottom of a 9 x 13 inch baking dish. Bake until golden, 20 to 25 minutes. Meanwhile, prepare filling.

FILLING:

1/4 c. all-purpose flour
1/2 tsp. baking powder
4 eggs
2 c. sugar
1/3 to 1/2 c. fresh lemon juice
1/2 to 1 tsp. lemon zest (yellow part only of skin)

Mix the flour and the baking powder in a small bowl. Combine the remaining ingredients in the processor work bowl, add the flour mixture and blend completely. Pour over hot crust and spread to the edges. Bake until set approximately 25 minutes. Cool before cutting.