For Turkey and Gravy:
Preheat the oven to 325 Degrees F. Place the turkey in a roasting pan. Remove the neck and innards from the cavity. Place the neck in the roasting pan; discard innards unless you wish to prepare them separately.
Tie the legs of the turkey together; fold and tuck wings under the body. Combine the butter and sage in a small bowl; brush mixture on the turkey. Season with salt and pepper and roast the turkey, uncovered, 1 1/2 hours hours. Baste turkey with pan juices, and then give the pan a 180-degree turn. Roast turkey another 1 hour and 15 minutes.
Insert an instant-read meat thermometer deep into an inner thigh of the turkey, not touching the bone. If it registers 170 Degrees F, the turkey is ready. If it doesn’t, baste the bird again and roast 15 to 30 minutes more, or until the 170 Degrees F temperature is achieved.
Transfer turkey to a large platter. Tent with foil and rest the bird until you’re ready to carve, at least 15 minutes.
To make gravy, skim excess fat from the pan drippings. Place the pan on the stovetop over medium-high heat. Add 3 cups of the stock and bring to a boil. Place the flour and the remaining stock in a bowl and whisk until smooth. Whisk the mixture into the pan and simmer until thickened gravy forms, about 5 minutes. Carve the turkey and serve the gravy in a sauceboat alongside.
Dressing:
Place bread in a large bowl. Melt 2 Tbsp. of the butter in a large skillet set over medium heat. Add onion, apple and celery and cook until tender, about 5 minutes. Spoon the onion mixture over the bread. Add the remaining ingredients and toss to combine.
Grease a 9" x 13" casserole dish with the remaining butter. Spoon the dressing into the casserole dish. (Dressing can be made to this point a few hours in advance. Cool to room temperature, cover with foil and refrigerate until ready to bake.)
Bake dressing in 375 Degree F oven for 20 minutes. Uncover and bake 20 minutes more, or until the dressing is hot and crisp and golden on top.
Note: Dried sage leaves are dried crumbled sage leaves, not finely powdered, ground sage.Dried sage leaves are sold in bottles in the spice and herb aisle.