Chop rosemary, mushrooms and place over beef. Drizzle over olive oil, balsamic vinegar and season. Enclose in tinfoil and cook 15 minutes for every 500gms of meat.
Remove from oven and rest for 10 minutes. Mix pan juice with red wine, mushrooms and thicken with cornflour mixed with water.
Serve with the gravy poured over the top.