PERSIAN SWEET-AND-SOUR CHICKEN SOUP

1 large onion, diced small
4-5 T butter
1 T ground coriander
1 1/2 t each cumin, cayenne, cinnamon
3/4 C long-grain rice
1/2 C finely chopped pitted prunes
1/3 C finely chopped dried apples or pears
11 C chicken stock
2 C finely chopped chicken, white meat (raw or cooked, I guess)
1/2 C cider vinegar or white wine vinegar
1/2 C toasted walnuts, finely ground
Salt and pepper to taste
1/2 C finely chopped fresh parsley
1/2 C finely chopped fresh mint
In a heavy-bottomed 6-quart saucepan, cook onion in butter over moderate heat for 5 minutes, stirring frequently. Add spices, rice, fruit, and chicken stock. Bring to a boil over high heat. Reduce heat to moderate and cook for 20-25 minutes, stirring occasionally.
Add chicken, vinegar, and walnuts. Cook for 10 minutes or until chicken is just cooked through. Season with salt and pepper. Garnish each portion with mint and parsley just before serving.