Blend flour, butter and powderd sugar with fingertips until well mixed. Pat evenly into the bottom of an 8-inch square baking pan. Bake for 20 minutes at 350°F
Meanwhile, beat together eggs, granulated sugar, baking powder, fresh lemon juice and a dash of salt. Pour over baked crust and return to oven for 20-25 minutes at same temperature.
Cool on rack. Cut into squares. Sprinkle with soft powdered sugar.