Preheat oven to 350 degrees.
For the crust, place the butter in a mixing bowl and microwave for about 30 seconds, or until slightly soft. Add all of the crust ingredients to the bowl and mix together with a pastry knife or two forks and blend until just incorporated. Place the crust mixture into the bottom of a 9x13 pan that has been sprayed with cooking spray.
Press the crust evenly into the bottom of the pan. Bake the crust for 15-20 minutes or until lightly golden brown. Once cooked, remove from the oven and set on aside while you make the filling.
For the filling, whisk together all of the ingredients until smooth. Make sure and measure the lemon juice carefully. If you add too much juice your bars won't set up. An exact cup is important. If you need to substitute a small portion of the juice with bottled that is fine but not ideal. Pour the filling mixture over the crust and return to the oven and bake for about 20-25 minutes, or until the mixture sets up firmly.
Remove the bars from the oven and let sit for 5 minutes. Once they have rested, dust the top of the bars with a thin layer of powdered sugar. If you like extra sour flavor, dust the top with a lemonade dry powder mix for extra sour power ;) A brand like countrytime lemonade mix works perfectly!