Line crock with slow cooker liner or spray with cooking spray.
Place the onion slices at the bottom of the crock.
Place ribs in slow cooker, meat side towards the side of the crock so the ribs line the crock. It’s OK if the rib ends overlap.
Wash the sweet potatoes. Pierce each sweet potato a couple of times with a fork. Wrap in aluminum foil and place in the middle of the crock between the two racks of ribs.
Place the lid on the crock. Cook on low for 6 to 8 hours or high for 4 to 6 hours until the meat on the ribs is falling off and the sweet potatoes are soft.
Remove the foil from the sweet potatoes and serve on the side or make into a sweet potato mash.
Serve the BBQ pork ribs with a little juice from the crock and/or barbecue sauce.