Trim the pork spareribs to be St. Louis-style ribs and remove the membrane from the bone side of the ribs.
Season the bone side first with the barbecue rub and the salt (if needed) then flip over and season the meat side.
Prepare the grill for two-zone grilling with hot coals on one side and nothing on the other.
Place the ribs on the side of the grill with no coals and place a chunk of smoke wood on the fire. Target internal temperature of the grill is 300° F.
Smoke the ribs for 90 minutes.
Prepare a foil boat for each slab by taking a piece of Reynolds Wrap Heavy Duty Foil that is a little longer than twice the length of each slab and fold it in half.
Add half the butter to each boat and half the barbecue sauce or apple butter.
Place the ribs meat-side down and then tighten up the foil around the ribs, leaving the top open.
Place the foil boat back on the indirect side of the grill and add another chunk of smoke wood over the coals if needed.
Once the bones stick out more than half an inch, remove from the boat (reserving the buttery slurry in the boat) and place the ribs meat-side down over the hot fire.
Sear quickly until there is a little char on the ribs and then place on a platter.
Slice the ribs and pour the butter slurry over the ribs. Enjoy!