2 Tablespoons kosher salt
1 Tablespoon garlic salt
1 Tablespoon paprika
1/2 teaspoon cayenne pepper
1 teaspoon freshly ground black pepper
8 pounds baby back ribs (8 racks) or spareribs (4 racks)
Chicken broth (or water)
1-2 cups barbecue sauce (store-bought or home-made)
Preheat oven to 300 degrees. Mix together rub ingredients in small jar. Place each rack of ribs on a double layer of foil. Sprinkle rub over ribs, both sides. Wrap racks individually and divide between 2 baking sheets. (Keep reserved rub in jar if you are only making half a recipe of ribs).
Bake ribs until very tender, about 2 hours for baby back ribs, 3 for spareribs. Carefully unwrap ribs (pour juices into Pyrex cup and reserve). Cool ribs completely. You can bake the ribs up to 3 days ahead. Cover and chill juices. Re-wrap ribs in foil and chill.
Heat gas grill to high (or build medium-hot fire on charcoal grill). Add broth or water to juices to measure 1 1/2 cups. Whisk in barbecue sauce.
Grill ribs, basting with barbecue sauce mixture and turning frequently until nicely glazed and charred in places and heated through, about 10 minutes. Transfer to cutting board and cut between ribs to separate. Serve with additional sauce.