For the cabbage soup, chop the onion and sauté in butter with the cabbage strips. Pour in the soup, season with salt and pepper and cook on low heat for 20 minutes with the lid closed. Strain the liquid and set aside.
Layer the toast, cooked cabbage and the cheese slices in an oven-proof terrine or gratin dish. Drizzle with the soup set aside.
Place the bacon slices on top of the soup and sprinkle with the grated cheese. Bake the cabbage soup in the oven (220° Celsius) for 20 minutes.