Quarter the cabbage, then slice into 1/2- 1cm wide strips, working from tip to root and discarding the core.

Heat the oil in a large, heavy-based frying pan over a high heat and cook the onion and cabbage for 5-6 mins, stirring until the cabbage starts to catch a little in places. Lower the heat, add the butter, some salt and pepper and cook for a further 4-5 mins until the cabbage is tender. Add the vinegar or lemon juice, check the seasoning and serve straightaway.