Polish Wild Mushroom Soup - cooking recipe

Ingredients

1/4 lb dried wild mushrooms, preferably boletus edulis (I use porcini)
9 cups beef stock or 9 cups canned reduced-sodium beef broth
1 cup butter (not margarine)
1 cup finely chopped onion
1 tablespoon cornstarch
salt
white pepper
sour cream
chopped fresh parsley

Preparation

Cover mushrooms with cold water and soak overnight.
Drain the mushrooms reserving the soaking liquid, strain the liquid through a fine cloth.
Rinse the mushrooms in cold water to remove any remaining sand then slice into strips.
Add the mushrooms, 8 cups of of the beef stock and the soaking liquid to a 3 quart saucepan, bring to a boil, reduce heat and simmer over low heat 4 hours.
Melt the butter in a heavy skillet, add the onion, saute until golden brown then add to the soup.
Whisk the cornstarch with the remaining cup of beef stock, add to the soup, stir and simmer until slightly thickened.
Season to taste with salt and pepper, ladle into individual bowls, top each with 1 tbs sour cream and sprinkle with parsley.