Slow Cook:8 hrs to 10 hrs (low) or 4 to 5 hours (high)
Trim fat from ribs. For rub, in a small bowl combine paprika, brown sugar, pasilla pepper, salt, garlic powder, coriander, mustard, celery salt, black pepper, and cayenne pepper. Generously sprinkle rub over both sides of ribs; rub in with your fingers. Place ribs in a 5- to 6-quart slow cooker, cutting to fit.
In a small bowl combine broth and 1/4 cup of the barbecue sauce. Add to slow cooker.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours.
Preheat broiler. Line a baking sheet with foil and transfer ribs, meaty sides up, to prepared baking sheet. Brush with the remaining 1/2 cup barbecue sauce. Broil 6 to 8 inches from heat for 5 to 8 minutes or until sauce begins to brown.