Place the barley in a bowl, cover well with cold water and allow to soak for 1 - 2 hours. Drain the barley and rinse under cold running water. Bring a pan of water to a boil, add the barley and cook for 15 minutes, or until tender. Drain the barley and set aside.

Trim any excess fat from the meat, then cut the meat into small cubes. Half fill a medium saucepan with salted water and bring to a boil. Add the lamb and cook for 2 minutes, then drain and plunge the lamb into a bowl of cold water. This process will give clarity to the soup and further remove traces of fat. Rinse the pan, half fill with salted water once more and bring to a boil. Add the meat, reduce the heat and simmer for 30 - 40 minutes, or until the meat is tender. Strain, reserving the meat, and measure the cooking liquid to 1 quart, adding extra water if necessary.

Place the butter in a large saucepan and melt over medium heat. Add the diced vegetables to the pan and cook, stirring frequently, until tender but not colored. Drain the vegetables and wipe out the pan with paper towels. Replace the vegetables, then mix in the lamb, barley and peas. Add the measured stock and bring to a boil. Reduce the heat and simmer for 30 minutes, while frequently skimming the surface to remove excess fat and impurities. Season to taste with salt and freshly ground black pepper and serve the soup with a sprinkling of parsley to garnish.