How to Make It
In a pot, heat the oil. Add the mushrooms, onion, carrots, celery, garlic, thyme, rosemary, bay leaf and peppercorns and cook over high heat until the vegetables are softened, 15 minutes. Add the Marsala and cook until evaporated, about 5 minutes. Add the water and bring to a boil. Simmer over moderate heat until reduced to 6 cups, 2 hours. Strain the stock, pressing down on the solids.