Wash potatoes thoroughly and boil in boiling water for 20-25 minutes. In the meantime, wash or grate the mushrooms, if necessary, clean them and dice them. Peel and finely dice the onion.
Wash the marjoram, dab dry, put something aside for garnishing. Fry the mushrooms in 2 tablespoons of oil until golden brown. Add onion and marjoram, fry briefly, add cream cheese, remove from heat, mix well with the mushroom mixture.
Season to taste with salt and pepper. Drain potatoes, rinse with cold water, peel and cut into pieces. Rinse chicken filets, dab dry. Cut a pocket on one side. Season with salt and pepper.
Fill the fillets with the mushroom mass. Fix with toothpicks. Heat 1 tablespoon of oil and fry the fillets for about 6 minutes on each side. Clean spring onions, wash them and cut them diagonally into wide rings.
Heat the fat in a pot, dust with flour and sauté while stirring. Stir in stock and milk bit by bit, bring to the boil. Season to taste with salt, pepper and mustard. Add potatoes and spring onions and warm up in the hot sauce.
Serve garnished with the chicken fillets and the marjoram set aside.