Peel and finely dice the onions. Knead minced meat, egg, half of the onion cubes and grated toast well. Season to taste with salt and pepper. Cut cheese into 8 cubes. Form 8 meatballs from the dough and press 1 corner of cheese in the middle of each.
Heat 2 tablespoons of oil in a frying pan and fry the meatballs in it at medium heat for about 15 minutes. Heat the rest of the oil in a frying pan and sauté the remaining onions in it. Clean, wash, halve and sauté the mushrooms.
Deglaze with cream and let it boil down a little. Season to taste with salt and pepper, stir in the sauce thickener and let it boil up briefly. Arrange mushrooms and meatballs on a preheated plate.
Sprinkle with cut cress and coloured pepper.