In small bowl, place raw cashews and add 2 cups boiling water. Let soak while preparing soup.
In large soup pot on medium, heat avocado oil. Add leeks and onions and saute for 5 minutes, until onions are translucent. Add garlic and sliced mushrooms and saute for a further 5 minutes, then add sherry vinegar, broth, and thyme sprigs. Bring soup to a boil, then reduce to a simmer for 10 minutes.
Remove pot from heat and discard thyme sprigs. With immersion blender, blend mushroom broth mixture well. Alternately, ladle all into blender and blend until smooth before returning to soup pot.
Drain water from cashews and add cashews to high-speed blender. Add 1 1/2 cups blended mushroom mixture to cashews and blend to create smooth cashew cream. Slowly whisk cashew cream back into remaining mushroom mixture in soup pot and bring to desired temperature. Enjoy!