Prepare the chicken by removing the bag of giblets and the neck from inside the cavity. Discard or save to make stock later.
Mix softened butter and garlic in a small bowl. Using your hands, smear the butter all over the bird and underneath the skin.
Place the chicken breast side up in a dutch oven that will accommodate it with room to spare.
Gently, slide herbs underneath the skin. Put the remaining herbs and onion halves inside the cavity.
Squeeze out both lemon halves over the bird and place inside cavity. Season the top of the bird with generous pinches of kosher salt and pepper.
Place the dutch oven (uncovered) in the oven for 15 minutes.
Baste the chicken, then return to the oven. Reduce heat to 350 and continue cooking UNCOVERED for approximately 20 minutes PER POUND, or until internal temperature reaches 165 degrees (about 1.5 hours for a 4.5 lb. chicken).
Allow the chicken to rest for 10 minutes before carving.
The bird should be golden brown all over with a crisp skin and have buttery, lemony juices of a nut-brown color in the bottom of the pan.