Directions

1. In a small bowl, combine mustard powder, paprika, celery salt, onion powder, red-pepper flakes, garlic powder, celery seed, and 1 teaspoon salt. Rub slabs on both sides with the spice mixture, and refrigerate, loosely covered, for 2 hours.
2. Preheat oven to 300 degrees. Stack slabs on a double layer of aluminum foil; tightly wrap. Place on a rack on a baking sheet. Cook until meat pulls away from the bone and is easily pierced with the tip of a sharp knife, 1 to 1 1/2 hours.
3. Heat grill to medium-high; lightly oil grates. Carefully remove ribs from foil, pouring off any liquid. Brush generously on both sides with rib sauce; grill ribs until sauce begins to bubble and brown around the edges, 4 to 5 minutes per side. Serve ribs with any leftover sauce, if desired.