Cut the cabbage into quarters and discard the outer leaves. Cut away the hard central core and shred the remaining cabbage finely.
Heat the oil in a large heavy based pan and cook the onion on a medium low heat until softened. Add the cabbage to the pan along with the vinegar, apple juice, berries and salt. Bring to a simmer.
Transfer to a sterilised Kilner® Jar and store in the fridge.
