Melt the butter in a large, heavy-based pan, add the onion and cook gently for 5-10 minutes until soft. Stir in the mixed spice.
Add the sliced cabbage, clementine halves, cinnamon stick, red wine vinegar and port. Sprinkle over the sugar, season with a little salt and stir well.
Bring to the boil then cover with a lid. Reduce the heat and simmer gently, covered, for 45 minutes or until tender.
Remove the clementine halves and cinnamon stick to serve (or leave as a decorative garnish if you wish).
Cook's tip: If clementines are not in season, you can use Sainsbury's sweet and juicy easy peelers instead.