Season the schnitzel, fry them and place them side by side in a greased baking dish. Sauté the onions in the pan, add ham and mushrooms. Fry everything briefly, season and distribute over the schnitzel. Pour the cream over it and chill overnight.
The next day, place in the oven preheated to 175 degrees and bake for about 45 minutes. Spaetzle tastes best with it.