Melt the butter in a small saucepan. Add the zest and juice of the lemon AND orange, and one teaspoon of thyme leaves to the butter mixture. Set aside.
Prep the turkey by removing any giblets and wash the turkey inside and out with cold water. Pat dry. Place the turkey into a large roasting pan. Very liberally season the turkey inside and out with salt and pepper.
Stuff the cavity with the bunch of thyme, halved lemon, quartered onion, and the halved garlic.
Brush the outside of the turkey with the butter thyme citrus mixture and sprinkle with a little more salt and pepper.
Tie the legs together with string and tuck the wing tips under the body of the turkey.
Roast the turkey about two and half hours, or until the juices run clear when you cut between the leg and the thigh. Internal temperature, when read with a meat thermometer in the thickest part of the turkey, should reach 170 degrees
Remove the turkey to a cutting board and cover with aluminum foil. Rest for at least 20 minutes before carving.