Preheat the oven to 180C/356F/gas 4. Work out the cooking time for your Fore Rib: If you prefer rare beef, cook for 20 minutes per 450g, plus an extra 20 minutes. For medium rare, cook for 25 minutes per 450g, then an extra 25 minutes. Or if you like beef that is well done, cook for 30 minutes per 450g, plus an extra 30 minutes. Let the Rib rest for 10 minutes before carving and don't forget the Horseradish Sauce!