Place the potatoes, 8 garlic cloves, onion, and carrots, in a large cast iron pan or roasting pan. Toss with avocado oil, salt, pepper and spread out on pan. Make a small hole in the middle for the chicken to be placed.
Prepare the butter spread by finely chopping 1 teaspoon of both the fresh thyme and the sage, and 1 tablespoon of the scallion, and mincing 1 garlic clove. In a small bowl add fresh herbs, garlic and softened butter to combine.
To prepare the chicken remove the giblets and remove any excess fat or feathers. Salt and pepper both the outside and the inside of the chicken. add remaining scallions, thyme and sage to the cavity. Tie the legs together with kitchen string and tuck the wing tips under the body of the chicken. Place chicken in the middle of the vegetables and spread the herb butter all over the skin of the chicken.
Place in the pre-heated oven and roast until chicken registers 165, or until juices run clear, about 1 hour and 10 minutes.
Let chicken rest for 15 minutes before slicing and serving.