In a large stockpot or Dutch oven, 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, about 1 1/2 hours. Add more water to adjust for any evaporation; skim the surface of the soup as necessary.
Remove meat from broth; cut meat from bone and cut in small pieces. Discard the bones and return the meat to the soup. Continue simmering.
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 for about 10 minutes, or until the vegetables are tender. Season with salt and pepper to taste. Serves 8.