This recipe was also featured on "Mad Hungry with Lucinda Scala Quinn."
Preheat oven to 325 degrees. Combine butter, sugar, salt, water, and vinegar in a Dutch oven or an ovenproof pot over medium heat. Bring mixture to a boil, stirring until butter melts and sugar dissolves.
Add cabbage, and toss to combine. Cover and place in oven. Bake, stirring once halfway through, until cabbage is wilted and tender, 1 hour and 50 minutes.
Stir in jelly and apple, cover, and bake 10 minutes more. Let stand, covered, until ready to serve (or for up to 1 hour; rewarm gently over low heat).