Cook barley in stock until tender, then add 4 1/2 cups water, soy sauce and sherry.
Heat oil in a frypan and saute onion and garlic gently until onion is transparent. Add mushrooms and cook until tender. Add to barley, cover and simmer for 20 minutes on low heat.
Season to taste. Serve with a dollop of light sour cream or cream if desired.
This recipe can be made in the slow cooker. Reduce soy sauce and sherry amount to 2 tablespoons. Simply saute the onions and garlic and add to slow cooker pot with uncooked barley and remaining ingredients. Cook on low for 6 hours or high for 4 hours. If preferred, this soup can be blended at the end of cooking to make a smooth soup. Alternatively, half could be pureed and stirred back into the remaining soup to keep some texture in the dish.