Preheat oven to 450°.
Discard gizzards and rinse chicken inside and out.
Pat dry, place breast side up in an ovenproof skillet and salt and pepper the inside of the chicken.
Gently pull the skin away from the meat and push the softened butter in between. Make sure to get back to the back of the chicken and down the sides.
Rub the outside of the chicken with butter too.
Squeeze the juice of ½ of the orange on top of the chicken and put that half in the cavity.
Stuff the cavity with the remaining orange, onions and ½ head of garlic.
Salt and pepper outside of chicken.
Place in oven and cook for 15 minutes. Then turn heat down to 375° and cook for about 45 min to 1 hour more. Thermometer should read 170° when inserted into the thigh and juices should run clear.
Baste the chicken with the pan juices several times throughout cooking and rotate once.
Let chicken rest, covered with foil before serving.