- 4 tablespoons unsalted butter
- 2 medium onions, thinly sliced
- 3 pounds green cabbage, cored and thinly sliced
- 1 large tart green apple, such as 'Granny Smith,' peeled, cored, and chopped
- 1 cup apple cider
- 1/3 cup cider vinegar
- 2 tablespoons packed light-brown sugar
- 1 tablespoon coarse salt
- 1 teaspoon freshly ground pepper
- 9 knockwurst
- Whole-grain mustard, for serving
- Melt butter in a large heavy-bottomed pot over medium-low heat. Add onions; cook, stirring occasionally, until very soft and golden brown, about 18 minutes.
- Stir in cabbage, apple, cider, vinegar, sugar, salt, and pepper. Cover; cook, stirring occasionally, until cabbage is very soft, about 1 hour.
- Tuck sausages into cabbage; cover pot. Cook until heated through, about 20 minutes. Serve with mustard.