Saute butter, leeks, onion, and garlic until clear. Add mushrooms (except the 8 reserved chopped mushrooms), savory, oregano, sherry, stock, tomato paste and bay leaf. Simmer for 30 minutes or so.
Strain out the vegetables.
Stir the reserved mushrooms and spinach leaves into the broth, and cook until spinach is wilted. Add salt and pepper to taste. Serve garnished with Parmesan cheese if desired.
