Wash and roughly chop the onion, celery and carrots into large pieces and place into a roasting tray
Season the meat with black pepper and a little salt and lay on top of the vegetables. Put in the oven and cook for about 20 mins until the vegetables are nicely browned and then add enough water to cover the vegetables well and return to the oven (this will be the base for your gravy). You will need to keep an eye on the water and top up when necessary. Allow 20 minutes per 450g plus 20 minutes extra, basting from time to time.