Pat the ribs dry with paper towels, flip bone side up, and remove as much of the thin membrane as you can by loosening a corner with a butter knife and pulling it off with a paper towel.
Spread a thin layer of yellow mustard over both sides of the ribs. Sprinkle the dry rub evenly all over, pressing it into the meat so it sticks and forms a solid coating.
Place the seasoned ribs on a tray and refrigerate for at least 1 hour so the rub can start to penetrate the meat, or up to overnight for more flavor.
Lay a large sheet of heavy-duty foil on the counter and place the ribs meat side up in the center. Add a small splash of apple juice and Worcestershire sauce around the ribs (if using), then wrap tightly, sealing the foil well to trap steam.
Preheat your grill to about 275°F using indirect heat. On a gas grill, turn on one or two burners and place the ribs over the unlit side; close the lid and let the temperature stabilize.
Set the foil-wrapped ribs over the indirect zone, close the lid, and cook for about 2 hours, turning the packet once halfway through to cook evenly.
Carefully transfer the foil packet to a tray and open it away from your face. The ribs should be more flexible and the meat slightly pulled back from the bone ends; if they still feel very stiff, rewrap and cook 15–30 minutes longer.
Adjust the grill to maintain 275–300°F. Place the unwrapped ribs meat side up over indirect heat and brush on a thin layer of BBQ sauce.
Cook for 30–45 minutes over indirect heat, brushing with more sauce every 10–15 minutes until the sauce has thickened, darkened slightly, and clings to the meat.
For a little char, move the ribs briefly over direct heat for 1–2 minutes per side, watching closely so the sauce does not burn.
Check for doneness: lift the rack from the center with tongs; it should bend easily and show small cracks between the bones, or register about 190–203°F in the thickest meat between the bones.
Transfer the ribs to a cutting board, rest for about 10 minutes, then slice between the bones into individual ribs and serve with extra BBQ sauce.