1Preheat oven to 350 degrees Fahrenheit.
In a medium bowl, combine butter, 2 cups flour and powdered sugar using a pastry blender. Press the mixture into the bottom of a 9 x 13-inch baking pan that has been sprayed with non-stick cooking spray. Bake for 13 minutes. Remove from oven.
2Meanwhile in a separate bowl, combine the lemon juice, eggs, sugar, baking powder and remaining 4 tablespoons flour; whisk until smooth.
3Pour lemon mixture over the baked crust and bake an additional 25 to 30 minutes. Remove from the oven and cool completely.
Sprinkle with sifted powdered sugar and cut into bars.