In a large stockpot, cover the lamb with cold water; bring to a boil. Add the barley, partially cover the pot, and simmer until the meat and barley is tender, 1 1/2 hours. Add more water to adjust for evaporation; skim the surface of the soup as necessary..
Remove the meat from the broth. Cut the meat away from the bone, discard the bones, and return the meat to the soup.Continue simmering the soup.
In a skillet, melt the butter over medium heat. Add the carrots, turnip, celery, and onion and cook stirring often for 10 minutes.
Add the vegetables to the soup. Simmer until the vegetables are tender, about 10 minutes more. Season with salt and pepper to taste.
Source: New York Cookbook, Molly O'Neill, 1993