4 cups apple cider
2 tablespoons cider vinegar
4 tablespoons (1/2 stick) unsalted butter, at room temperature
kosher salt and black pepper
4 stalks celery, halved crosswise
4 carrots, peeled and halved crosswise
2 medium onions, peeled and halved
1 12-pound turkey—thawed if frozen, giblets discarded, and patted dry
1 tart apple (such as Granny Smith or Pink Lady), halved
8 sprigs fresh thyme 8 sprigs fresh sage
Heat oven to 375° F. Make the cider glaze: In a large skillet, boil the cider until reduced to about ¾ cup, 25 to 30 minutes. Add the vinegar, 2 tablespoons of the butter, 1 teaspoon salt, and ½ teaspoon pepper and stir until the butter has melted.
Meanwhile, in a large roasting pan, scatter the celery, carrots, and onions; add 1 cup water. Season the turkey cavity with 1/2 teaspoon each salt and pepper and stuff with the apple, thyme, and sage. Tie the legs together with twine and tuck the wings underneath the body. Place the turkey on top of the vegetables, rub with the remaining 2 tablespoons of butter, and season with 2 teaspoons salt.
Roast the turkey, basting every 30 minutes with the pan juices, for 2 hours. Continue roasting, basting every 15 minutes with the cider glaze, until a thermometer inserted into the thickest part of a thigh registers 165° F, 30 to 60 minutes more. (Tent the bird loosely with foil if it browns too quickly; add 1 cup water to the pan if the vegetables begin to scorch.)
Carefully tilt the turkey to empty the juices from the cavity into the pan. Transfer the turkey to a cutting board, tent loosely with foil, and let rest for at least 30 minutes and up to 1 hour before carving. Reserve the pan and its contents for Bourbon Gravy.