Pressure Cooker Portobello Barley Soup

I dug this recipe out of a discarded library book (unfortunately I can't tell you which one because I tore the page out and the book's title isn't listed on the page)... it has quickly become a favorite!

Ingredients:
3 T olive oil
1 onion, chopped
2 stalks celery, chopped
1 carrot, chopped
2 t minced garlic
1 bay leaf
1-2 portobello mushroom caps, chopped (I use two-- the more the merrier!)
1/2 pound fresh mushrooms of any type, sliced
1/2 cup pearl barley
6 cups water (or use chicken stock for a richer taste)
2 t salt
1/4 t pepper
Fresh parsley for garnish

• Heat the oil in the pressure cooker; saute the onion until soft (about five minutes), then add celery, carrot, garlic, and bay leaf. Cook for ten minutes or until onion begins to turn golden, stirring often.
• Add all of the mushrooms and cook for 5 minutes, until the mushrooms release their moisture. Stir in barley, water, salt and pepper.
• Lock the lid and cook on low for 20 minutes.
• Remove from heat and allow the pressure to drop naturally.
• Ditch the bay leaf and serve garnished with fresh parsley.