In a small bowl, combine mustard powder, salt, garlic salt, onion salt, celery salt, and allspice.

Using a sharp knife, make several deep slits in the roast to form pockets of different depths. Rub seasoning mixture into meat and pockets. Set aside, can sit in fridge for up to two hours.

Place roast directly on smoker rack and lay rosemary on top. Smoke at 225F – 250F for up to three hours (longer if roast has bone in) until meat thermometer registers 130F in thickest part of roast for medium-rare finish. Let rest for 15 minutes before carving.