Remove the membrane. Flip the rack bone-side up. Slide a paring knife under the silver membrane at one end and lift a corner. Grip with a paper towel and pull steadily until the membrane peels off completely.
Make the dry rub. In a small bowl, combine the kosher salt, brown sugar, smoked paprika, garlic powder, and black pepper. Stir to blend.
Season the ribs. Pat the ribs completely dry with paper towels. Brush both sides with a thin layer of yellow mustard if using. Sprinkle the dry rub generously on both sides and press it into the meat.
Dry brine (optional but recommended). Place the seasoned ribs uncovered on a plate and refrigerate for at least 1 hour, ideally overnight, for the deepest flavor and juiciest results.
Preheat the air fryer to 320°F for 3–5 minutes.
Cut to fit. If using a basket-style air fryer, cut the rack in half so it lies flat. For oven-style air fryers, a full rack usually fits on the tray.
First cook. Place the ribs meat-side up in a single layer. Do not stack or overlap. Air fry at 320°F for 25 minutes.
Flip and sauce. Open the air fryer, flip the ribs bone-side up, and brush the bone side with BBQ sauce. Cook 5 minutes more.
Final glaze. Flip ribs meat-side up and brush the top with BBQ sauce. Cook another 5 minutes, or until the internal temperature reaches 195–203°F using an instant-read meat thermometer.
Rest. Remove ribs from the air fryer and tent loosely with foil. Rest 5–10 minutes to let juices redistribute.
Serve. Slice between the bones and serve with extra BBQ sauce on the side.