Clean, quarter, wash and cut the savoy cabbage into strips from the stalk. Peel and halve the onion and cut into strips.
Heat 1-2 tablespoons of butter in a saucepan. Brown onion and cabbage in it. Add 200 ml water and broth and bring to the boil. Cover and stew for about 10 minutes. Season to taste with salt and pepper.
Cut the rolls into slices of about 1/2 cm thick. In a pan without fat, roast briefly on each side.
Mix sour cream, mustard and 2-3 tablespoons of water. Cut meat loaf into approx. 6 slices, then halve.
Grease an ovenproof dish. Alternately layer rolls, savoy cabbage and meat loaf. Spread mustard cream on top. Bake in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for approx. 20 minutes.