Non-stick cooking spray
1 c. plus 4 1/2 tsp. sifted flour
1/3 c. plus 1 tbsp. sifted confectioners' sugar
1/2 tsp. baking powder
1/4 c. cold butter, cut into bits
1 lg. egg, separated
1 tsp. grated lemon rind
2 tbsp. ice water
2/3 c. sugar
1/4 c. lemon juice
1/8 tsp. salt

Heat oven to 375 degrees. Coat 8 x 8 x 2 inch dish with spray. In medium bowl mix 1 cup flour, 1/3 cup confectioners' sugar and 1/4 teaspoon baking powder. Use fork and cut in butter until it resembles meal. Sprinkle ice water and mix until dough holds when pinched. Pat dough in bottom of dish and bake 20 minutes. In small bowl, beat egg white, sugar and juice at moderate speed for 2 minutes until light. Whisk in 4 1/2 teaspoons of flour, lemon rind, remaining 1/4 teaspoon baking powder and salt. Pour over cooked dough, return to oven and bake 20 minutes more until topping has set. Place pan on wire rack, cool 1 hour. Cut into squares and sprinkle remaining confectioners' sugar over top.