Cut duck in serving-size pieces & place in porcelain, stainless steel or glass baking dish. Add onions, parsley, bay leaf, thyme, garlic, green peppercorns, cognac & wine; stir to coat duck well. Let stand 4 hours at room temperature, turning pieces frequently. Then lift out & pat dry; reserving marinade. Heat oil in heavy skillet over high heat.
Add duck & cook until evenly browned on all sides, turn as needed (usually takes 10-15 minutes). Add reserved marinade & mushrooms. Reduce heat to low, cover & simmer 1 hour or until duck is tender & leg joints wiggle easily. Season with salt.Servings: 4