Place turkey in a large pan, bowl, or tub. Remove the neck and innards and save to make a gravy, if desired. Season the inside of the turkey with 1 1/2 tablespoons salt, and then the outside with the rest, until the entire surface of the bird has a thin coating of salt crystals. Transfer to the refrigerator, uncovered, and let brine for 12 to 24 hours.
Preheat the oven to 450 degrees F (230 degrees C). Set a large foil roasting pan over a sheet pan.
Cut the bread loaf lengthwise into two halves. Butter generously and place buttered-side up into the prepared roasting pan, pushing bread halves together so they are touching.
Remove turkey from the fridge and stuff sage, rosemary, and thyme into the cavity. Tie the legs together with kitchen string and place breast-side down on top of the bread, making sure turkey is as steady and straight-up as possible. Tuck wing tips up and over the drumette.
Roast in the preheated oven until an instant-read thermometer inserted into the thickest part of the thigh registers 165 degrees F (74 degrees C), about 2 hours. Let turkey rest for at least 15 to 20 minutes before carving.
In the meantime, cut bread into cubes and transfer onto a serving plate; keep warm as needed. Spoon juices onto the turkey, place it on top of the bread, and carve.