Slice leeks thinly, using white and palest green parts only. Heat margarine in large soup pot. Saute leeks, onions and mushrooms over medium heat until onion is translucent. Add potatoes, bay leaf and just enough broth to cover. Bring to a boil then cover and simmer until potatoes are tender (about 15-20 mins).

With a spoon mash SOME of the potatoes against the sides of the pot. Add milk and simmer over low heat for another 20 minutes. Season with salt and pepper. Stir in parsley/cilantro.