Melt the duck or goose fat in a very large heavy-based pan set over a medium heat, then tip in the red cabbage and onions. Sauté over a medium-high heat for about 5 minutes, until just beginning to soften.
Stir in the apple and cranberries, then add the red wine, pomegranate juice, redcurrant jelly, red wine vinegar and spices. Season to taste. Bring to the boil, stirring occasionally, then reduce the heat and simmer for about 1 hour, stirring every 20 minutes, until the cabbage is meltingly tender. Transfer to a warmed dish and garnish with pomegranate seeds (if using) to serve.