Rub salt under the skin. Place the salted meat into a vacuum bag, tucking herbs and garlic underneath, and seal.
Place the bagged meat on a perforated pan in steam oven, or in a sous vide bath, and cook for 3 hours.
While the turkey is roasting, combine the butter, salt, and pepper in a small bowl and set aside.
Smear the butter over the skin and broil until crisp and golden brown. Then let it rest before carving into thin slices for serving.