This soup is all about the mushrooms...there's no mistaking the difference between freshly-made mushroom soup and the stuff in a can! If you're feeling ambitious, make a stock yourself using 5 cups of water, sliced carrots, onions, thyme, and the veins scraped from the portabella mushrooms, stweing for 4 hours on low heat. Strain the vegetables out, and you'll have about 4 cups of stock remaining.