1 Wash and dry the meat and season with salt and pepper. Trim the leeks and spring onions and cut into rings. Peel and finely chop the garlic. Heat 1-2 tbsp oil and sweat the leeks, spring onions and garlic until the leek is soft but still retains a little bite. Season the leek and spring onion mixture with salt and pepper and stir in the mustard and chopped rosemary. Open out the meat, stuff with the mixture and then close the meat up around the stuffing. Tie with string. Heat the rest of the oil in a flameproof roasting tin on the hob and brown the meat on all sides. Peel the carrot, onion and celeriac and cut into pieces. Wash and roughly chop the parsley. Add the vegetables and tomato puree to the roasting tin and cook briefly, then add the parsley and stir in the wine and stock. Add the rosemary and put into a preheated oven (180 °C with top and bottom heat) for about 60 minutes, or until the meat is done. Then take the meat out of the oven and allow to rest for 10 minutes. Strain the sauce through a sieve, catching the liquid, season to taste and thicken with cornflour if you wish.