Add lamb bone, onion, carrots, garlic, rosemary, bay leaf, peppercorns, salt and vinegar to your slow cooker. Cover with water and set on low for 12 hours.
An hour before the broth is done, remove lamb meat that has fallen off the bone with a slotted spoon. Cut up the meat, cover, and store in the refrigerator.
After your broth is cooked, Place a strainer in a large pot. Now, lift the whole pot from the heating base of your slow cooker and slowly and carefully strain broth over the large empty pot, Discard the bones and vegetables.
Skim fat off the top of your broth. Add cut up meat back in along with scallions and dill. Adjust seasonings and simmer for 10 minutes. Serve hot.
I have a 6½ quart slow cooker. Add enough water to cover the bone with about one inch of water.