1. If using fresh chestnuts, cut a small portion from the tops of their shells and put them into a saucepan of cold water. Bring to the boil and simmer for 5 minutes.
2. Take the pan off the heat. As soon as the chestnuts are cool enough to handle, peel them, leaving them immersed until skinned.
3. If using dried chestnuts, pour hot water on them and leave them for 3 hours.
4. Put the chestnuts and the soaking water into a saucepan, bring them to the boil and simmer for 30 minutes. Drain them if neccessary.
5. Dice the bacon, finely shred the cabbage and peel, quarter and thinly slice the onion.
6. Heat the oil in a heavy saucepan on low heat. Put the onion and bacon and cook them until the onion is soft.
7. Fold in the chestnuts, cabbage and sage. Add the vinegar and cover the pan tightly.
8. Cook gently for 10 minutes.