Blend flour, butter and powdered sugar with fingertips until well mixed. Pat evenly into the bottom of an 8x8 inch baking pan. Bake for 20 minutes at 350 degrees. 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.