Using a sharp knife, trim any fat from the lamb and cut the meat into thin strips. Set aside until required.

Bring a large pan of lightly salted water to the boil and add the rice. Bring back to the boil, stir once, reduce the heat and cook for 10 - 15 minutes, until tender.

Drain the rice, rinse under cold running water, drain again and set aside until required.

Meanwhile, put the lamb stock in a large saucepan and bring to the boil.

Add the lamb strips, leek, garlic, soy sauce and rice wine vinegar to the stock in the pan. Reduce the heat, cover and leave to simmer for 10 minutes, or until the lamb is tender and cooked through.

Add the mushroom slices and the rice to the pan and cook for a further 2 - 3 minutes, or

until the mushroom is completely cooked through.

Ladle the soup into 4 individual warmed soup bowls and serve immediately.