Heat oil in large saucepan over medium-high heat. Add mushrooms, celery, onion, carrots and garlic; cook until onion is well caramelized and vegetables are somewhat tender, about 10 minutes. Deglaze with red wine. Add parsley stems, thyme, peppercorns and bay leaf. Simmer until wine is reduced by half, stirring constantly. Add reduced veal stock; bring to a boil, skimming surface.