1. trim the meat of visible fat and season it with salt and pepper. Place the onions in the bottom of the crock, then lay the meat on top of them.
2. Pour about a half cup of the barbecue sauce over the meat and flip it around to coat it. Cover and let it cook for 9 to 10 hours on low.
3. Carefully remove the cooked meat from the crock and pour out the fat and juices, retaining the onions. Using two forks, shred the meat into stringy chunks, discarding any fat.
4. Put the meat back in the crock, mix in the remaining barbecue sauce, and let it cook another half hour or so. (You could eat it now, but it's better if it soaks awhile.)
Serve on soft rolls, onions on the side.