In a soup pot, cook the mushrooms in the butter. One wants to cook the mushrooms in small batches as Julia Child states, don't crowd your mushrooms. If using portobello mushrooms slice them before cooking them in the butter. Cook 2-3 minutes on each side on medium heat.
Remove mushrooms from pan, add more butter and saute chopped onions till soft. Then add minced garlic to onions and cook for two more minutes on low heat.
Next add apple cider vinegar, herbs, bay leaf, and 4 cups chicken or vegetable broth. Bring to low simmer, cover & keep simmering for at least 20 minutes.
While the soup is simmering make the rue by mixing 1/2 cup broth or water and 1/4 cup arrowroot flour.
Once soup has simmered for 20 minutes stir in the cream. Keep soup on low heat and add the rue BUT add very slowly while using a whisk to stir the soup and continue stirring the soup till it thickens. Add salt to taste.
I use 1/2 of this recipe for my green bean casserole.
