Soak the rolls. Peel and finely dice the onions. Knead the mince, ground meat, squeezed bun, half of the onions, eggs, mustard, marjoram, pepper and salt.
Shape approx. 16 meatballs from the mixture with moistened hands. Place in another roaster or an ovenproof pan. Fry in a preheated oven (top / bottom heat: 200 ° C, fan oven: 175 ° C, gas: level 3) for about 25 minutes.
Clean, wash and slice the mushrooms. Fry in the hot oil in portions. Season with salt and pepper. Fry the remaining onions briefly as well. Pour 400 ml of water and the cream. Simmer over low heat for about 3 minutes, stirring frequently. Season again to taste and then thicken the sauce with a sauce thickener.
Pour the mushroom cream over the meatballs and stew in the oven for another 20 minutes. Arrange and garnish.