To make the rub: mix the salt, brown sugar, pepper, paprika, onion and garlic powders, and dry mustard in a small bowl and mix well.

Remove the thin membrane from the back of each rack by inserting a knife under it and pulling it away from the rib rack.

Sprinkle dry rub over both sides of the ribs, rubbing it onto the meat. Cover the ribs with plastic wrap and refrigerate them for 2 hours minimum.

For the basting sauce melt butter in a small saucepan over medium heat. Stir in the apple cider vinegar and soy sauce. Keep warm until ready to use.

Preheat oven to 300°F.

Place the ribs, bone side down, on an aluminum foil lined baking sheet. Cook the ribs for 45 minutes.

Brush with basting sauce, turn and brush again. Continue cooking the ribs 45 minutes to 1 hour longer until well browned and tender.

Brush with your favorite BBQ sauce, and broil the ribs until the BBQ sauce is browned and bubbling, a couple minutes per side.

Remove from the oven and let the ribs rest for a few minutes, then cut the ribs.