Heat a medium stock pot over medium-high heat. Once hot, add olive oil, onions, mushrooms, thyme and salt. Saute for 10-12 minutes until mushrooms are soft and onions are translucent. Add cashews and saute for an additional 2 minutes. Add the vegetable stock and bring to a simmer over medium-low heat. Simmer for 60-90 minutes. Place the immersion blender into the middle of the stockpot. Submerge the blender below the surface of the liquid, but above the bottom of the pot. Start the blender on its lowest speed, then quickly increase to its highest speed. Move the immersion blender around, including up and down, to blend the ingredients for approximately 1 minute or until desired consistency is achieved. Serve immediately, or cool in an ice bath and store in an airtight container in the refrigerator.