Preheat oven to 350.
For crust: Mix flour, butter and powdered sugar in a bowl until crumbly.
Pat into greased and floured 9 x 13 x 2 pan.
Bake at 350 for 15 to 17 minutes (until light golden). Cool.
For filling: Beat eggs until milky (lots of beating). Add lemon juice, sugar, flour and baking powder, mixing slowly until combined. Pour over cooled crust.
Bake at 350 for 20 minutes or until set. Gently jiggle pan to see if center is firm.
Remove from oven and sift additional powdered sugar on top.
Cool completely before cutting into pieces.