Remove outer damaged leaves and cut the cabbage in quarters. Cut away the hard core and then shred the cabbage finely across the leaves.
Melt the butter in a heavy saucepan and add the sugar. Stir just to blend and then add the wine vinegar. Add the shredded cabbage and toss well to mix the ingredients. Cover with a lid and leave to cook over very gentle heat. The slower the cabbage cooks the better it will taste and it can easily be left to cook for 2 hours. Stir or shake the pan occasionally.
When ready the cabbage should be slightly moist without any liquid being visible. Add the redcurrant jelly and toss to glaze the cabbage. Season to taste with salt before serving.