Cut the cabbage in half and soak in salted water for 15 minutes.
Heat the bacon fat in a large, heavy skillet and add the diced potatoes.
Cook over medium heat until lightly browned.
Add 2 chopped onions and cook until transparent, about 5 minutes.
Add cabbage and toss well with two wooden spoons, a la stir-fry.
When the cabbage starts to wilt, add salt and freshly-ground black pepper to taste and a splash of water and about 1 tablespoon wine vinegar.
Cover, with lid slightly askew, and simmer over low heat until tender (about 30-45 minutes).