Cut the pork into neat slices. Blend the flour, salt and pepper and use to coat the meat lightly. Heat the oil in a large nonstick frying pan, fry the pork slices on either side until golden brown and transfer to a casserole.

Add the onions, leeks and celery to the pan and fry gently for 10 minutes; do not allow the vegetables to brown. Spoon these vegetables over the pork then add the pepper and tomatoes.

Pour the lemon juice or vinegar, chicken stock and tomato puree into the pan; stir well to absorb any meat juices, season to taste, then spoon over the pork and vegetables.

Cover the casserole and cook in the oven for 40-50 minutes, or until the meat is tender.

The fillet is the leanest cut of pork and also the most tender – it is sometimes called tenderloin. For this dish it is not necessary to buy the fillet in one piece.