Put the oil in a large saucepan over a medium to high heat. Add the beef, diced onions, chillies and garlic and sweat them together. Drain off any excess fat if a lot comes off the beef. Drain the chopped tomatoes, but reserve the juice. Then add the chopped tomatoes and tomato purée to the pan, and a pinch of Maldon salt. Continue cooking for 10 minutes; if there’s any sign of it catching, add a little of the juice from the tomatoes. Add the cumin and cook for a further 10–20 minutes, or until the beef is tender. Put it in a serving bowl, check the seasoning and top with some coriander.