One hour before cooking the turkey, remove the poultry from the fridge. Discard the packaging and place the giblets and neck in a pot covered with water (if using).
Rinse the turkey with cold water and dry thoroughly with paper towels. Place it in a roasting pan and let the turkey rest for 45–60 minutes.
Preheat the oven to 425˚F.
Season the bird all over (inside and out) with the salt and pepper. Smear the butter over the top of the bird and in between the skin and breast meat. Place the onion, apple and thyme leaves into the cavity and tuck the wing tips underneath. Tie the legs together loosely.
Pour stock or water into the pan under the turkey. Roast the bird uncovered for 30 minutes. Reduce the oven temperature to 350˚F and baste the turkey with the pan juices.
After 1 hour baste the turkey again. Continue basting every 30 minutes until the turkey is cooked. If the skin is browning too quickly, tent it loosely with a piece of aluminum foil. Rotate the roasting pan 180 degrees each time you baste it to assist with even browning.
30 minutes before you think the turkey will be done, insert a meat thermometer into the thickest part of the thigh, but not too close to the bone. When the meat is done it should read 170˚F and release clear juices when the thermometer is removed from the meat.
Let the meat rest for 30–60 minutes, covered loosely in foil. Remove the foil and carve just before serving.