Remove any wilted or damaged leaves from the cabbage. Cut into quarters and remove the core. Slice the cabbage as thinly as possible with a sharp knife and place in a deep tray. Tie up the cinnamon and juniper berries in a piece of muslin cloth and add to the cabbage. Add the remaining ingredients except the butter and mix well. Cover with clingfilm and marinate in the fridge for 12 hours.
Preheat the oven to 140°C. Drain the cabbage and reserve the liquid. Melt the butter in a heavy-based saucepan, add the cabbage and sweat without colouring until it wilts. Add the reserved liquid and bring to the boil. Cover the saucepan with a lid, transfer the cabbage to the oven and cook for 2½–3 hours until the cabbage is tender and the juices have reduced to a syrup. Stir every 30 minutes. Remove the muslin bag from the cabbage and discard. Adjust the seasoning if necessary and check whether more Cabernet Sauvignon vinegar is required. The cabbage can be kept covered in the fridge for 4–5 days before using.