Prepare the brine according to recipe linked above.
Brine whole chicken for 8 hours. This is an optional step but highly recommended since it makes the meat so juicy.
Remove the chicken from brine.
Rinse it with cold water and pat it dry with paper towels.
Spatchcock the chicken by placing it breast-side down. Remove the backbone with kitchen shears. Open rib cage with your hands. Then, use a knife to score down the sternum to help flatten it. Flip the chicken over and use your hands to firmly push it down until chicken is completely lying flat.
Use your fingers to loosen the skin.
Spread half the butter under the skin, and spread the remainder all over the chicken.
Place the chicken flat on a baking tray, lined with foil paper.
Bake uncovered at 400 degrees F for 40-45 minutes or until an inserted thermometer into the thickest part of the chicken- breast and thigh reads 165 degrees F.
Remove form oven and let it rest uncovered 5- 10 minutes. Then, enjoy!