Heat the oil and butter in a large casserole dish. Add the sliced onion and cook gently for 15 minutes until soft, then add in the garlic and cook for another 2 minutes before adding into the cabbage, apple and vinegar. Mix well then stir in the redcurrant jelly, add the cinnamon and star anise, and cover with a tight-fitting lid. Cook over a low heat for 1-1.5 hours, stirring occasionally, until the cabbage is cooked. Cook without the lid for a few minutes if there’s liquid in the pan that you want to reduce. Then switch off the heat and leave the lid on until you’re ready to serve.