Mushroom Barley Soup

We got this recipe from a friend. It is high on my list of favourite soups.

1 ½ lb mushrooms (white button, baby portabella, or mixture of both)
1/4 cup butter or oil (prefer unsalted)
1 large onion chopped
1 leek, white and pale green parts only, chopped
8 cups broth
1 medium potato, peeled, diced small
1/2 cup chopped celery (use the top leaves too)
1 teaspoon minced garlic
1 large carrot peeled and thinly sliced
1/2 cup pearl barley
2 bay leaves
salt and pepper

Remove stems from mushrooms, slice caps, chop stems and set aside.
Melt butter in heavy large soup pot over medium heat and add onion, leek, carrots, celery, and garlic. Sauté until tender, about 8 minutes, stirring constantly.
Add mushrooms, cook 2 minutes.
Add chicken stock, barley, potato, and bay leaves and bring to boil over high heat. Reduce to low heat, cover and simmer about 35 minutes.
Season to taste with salt and pepper.
Remove bay leaves and discard.