For the red cabbage and potato gratin, first quarter the red cabbage, cut away the stalk and cut the rest into thin strips. Peel the onion and also cut into thin strips. Quarter the apples, cut out the core and cut the flesh into narrow wedges.
Brown the bacon cubes in hot oil. Add red cabbage, onion, apples and rice and sauté, turning, for three to four minutes. Deglaze with wine and vinegar and season with pepper and salt. Add the rosemary sprig and cook the red cabbage with the lid closed over medium heat for about an hour.
Butter an ovenproof dish and put the cooked red cabbage in it. Peel the potatoes and cut them into thin slices. Cover the red cabbage with them in the form of scales.
Pour the vegetable soup over it and put the butter in flakes on the potatoes. Season the potatoes lightly with salt.
Bake the red cabbage and potato gratin in the oven heated to 180 °C on the second lowest shelf for about 40 minutes.