Thaw the turkey in the refrigerator for 3 to 4 days. Remove the packaging, neck, and giblets, pat the turkey very dry, and allow it to sit at room temperature for 45 to 60 minutes before roasting.

Heat the oven to 325°F (165°C). Arrange the optional carrots and celery in the bottom of a large roasting pan, pour in the broth, and set a roasting rack over the vegetables.

Mix the softened butter, olive oil, kosher salt, black pepper, minced garlic, parsley, sage, rosemary, and thyme in a bowl. Carefully loosen the breast skin and spread about half of the herb butter underneath it, then rub the rest over the turkey.

Season the cavity lightly with salt and pepper. Place the quartered onion, lemon halves, and halved garlic head inside without packing the cavity tightly.

Tie the legs loosely with kitchen twine and tuck the wing tips beneath the bird. Set the turkey breast-side up on the rack in the prepared roasting pan.

Roast at 325°F for approximately 3 to 3 3/4 hours, beginning to check the temperature after about 2 1/2 hours. Baste once or twice with pan juices if desired, but avoid opening the oven repeatedly.

Insert an instant-read thermometer into the thickest part of the breast without touching bone; it should reach 160 to 165°F. Check the thickest part of the thigh as well, which must reach at least 165°F.

Transfer the turkey to a cutting board, tent it loosely with foil, and rest for 30 to 45 minutes. The temperature will usually rise several degrees during resting, and the juices will redistribute for cleaner, moister slices.