1 Season the pork. Heat 2 tbsp oil in a large, flameproof casserole dish and sear the pork in batches, until browned; set aside in a bowl. Add the wine to the pan and, as it bubbles up, scrape down the base of the pan with a wooden spoon to release all the caramelised juices. Pour over the pork and set aside.
2 Add the remaining 2 tbsp oil to the pan with the onions, cover and fry gently for 15 minutes, stirring now and then, until they are very soft. Add the garlic and chorizo; fry for 2-3 minutes. Stir in the paprika and cook for 1 minute, then add the tomato purée, tomatoes, stock, herbs, pork and juices. Season, cover and simmer for 1 hour.
3 Boil the vinegar and sugar in a small pan; reduce to about 1 teaspoon. Stir it into the casserole with the olives. Simmer uncovered for 20-30 minutes, until the pork is tender. Season and serve, with patatasfritas (fried potatoes), if liked.