This is a very simple recipe, well suited to endless variations. The best instance of it in my memory was on holiday in Greece when the butcher's mother let me point out exactly which piece of the side of pork I wanted. I did it with quince jelly that time.
Some other types of fruit that go well with pork are apricots (fresh, tinned, or dried and soaked), morello cherries (sour cherries), and mirabelles (very small plums).
Melt the butter in a large thick-bottomed pan. When it stops foaming put in the meat and quickly brown on all sides until you don't see any raw bits. If the meat has a fatty side, turn that side down. Turn down the heat. Sprinkle the meat with salt and pepper and add some liquid so it doesn't stick. Cover the pan.
Cook for about half an hour, turning occasionally to brown the meat on all sides.
Add the juice and some of the rind of the oranges, or the jam and some more liquid, or all of the contents of the jar of fruit. Cook for another half-hour or until the meat feels firm when you press on it and the juice flows clear when you prick it.
Take the meat out of the pan and put it aside on a wooden board.
If there's not enough liquid in the pan to make sauce, add some more stock, wine, fruit juice, water or a combination. Bring to a rolling boil. Mix a heaped teaspoonful of cornflour to a thin smooth paste with some water, add this to the juices in the pan and stir until it's boiling again. Taste the sauce and add flavourings if necessary.
Warm the meat in the sauce for a minute or so. Serve the meat on a flat dish and the sauce in a bowl.