3 tablespoons olive oil
1 large onion, chopped
2 garlic cloves, minced
1 teaspoon crushed red pepper flakes
1/4 cup balsamic vinegar
2 tablespoons brown sugar
6 cups finely sliced red cabbage
1 cup chopped and drained plum tomatoes from a can
6 cups chicken stock
Salt and freshly ground black pepper
1/4 cup finely chopped fresh parsley
Sour cream and finely chopped fresh chives, as accompaniments