Fry the schnitzel without breading, but do not let it get too soft. Steam the chopped onion in the frying fat until translucent. Mix the sweet / sour cream and creme fraiche and pour onto the onions.
Dice the schnitzel and ham. Put the cutlet pieces in an ovenproof dish, pour the ham over them and pour the sauce over them so that everything is well covered. Leave to stand overnight with the pot closed.
1 1/4 hours before serving, the pot is placed in the preheated oven at 200 °.