In a large pot, heat oil and saute the onions, carrots and celery until soft.
Add the garlic and half the mushrooms, and saute 3-4 minutes.
Add the broth, thyme, parsley and cashews. Simmer for 20-30 minutes. Add more broth as needed to reach desired consistency.
Return the soup to the pot and add remaining mushrooms. Bring to a boil, then simmer 3-4 minutes.