Heat oven to 350°F. In small bowl, mix flour, butter and 1/4 cup powdered sugar. Press in ungreased 8-inch or 9-inch square pan, building up 1/2-inch edge. Bake 20 minutes.
In small bowl, beat granulated sugar, lemon peel, lemon juice, baking powder, salt and eggs with electric mixer on high speed about 3 minutes or until light and fluffy. Pour over hot crust.
Bake 25 to 30 minutes or until almost no indentation remains when touched lightly in center. Cool completely, about 1 hour. Sprinkle with additional powdered sugar. For squares, cut into 5 rows by 5 rows.