1. In a large pot, heat olive oil on medium low and saute the onions with ½ tsp of the salt for 5 minutes.
2. Add in the baby portobello mushrooms and saute for another 3 minutes.
3. Season with the rest of the salt, black pepper, thyme and cayenne pepper then add in the vegetable broth and milk.
4. Simmer the soup on low for 25 minutes with the top partially on.
5. With an immersion blender, roughly blend the soup so that there is still texture.
6. Bring the soup to a boil and in a small bowl mix together the flour and water into a slurry.
7. Carefully whisk the flour slurry into the boiling soup, this will thicken the soup.
8. Return the soup to a low simmer for an additional 10 minutes with the top off. Stir in 1 Tbs of the parsley.
9. Serve immediately with fresh parsley and croutons.