Wash the schnitzel and pat dry. Fry in oil with turns and season with salt and pepper. Place them side by side in a baking dish.
Clean and wash the leek and cut into rings. Clean, halve or slice the mushrooms.
Fry the mushrooms in hot oil and season with salt and pepper. Dust the flour over it and sweat it. Add the stock and cream and bring to the boil while stirring. Add the leek and marjoram. Cover and simmer for about 5 minutes. Stir it every now and then.
Season the mushroom mixture with salt and pepper and pour over the schnitzel. Cover and braise in a preheated oven at 175 ° C for about 1 3/4 hours. After about 1 hour, remove the lid and cook until the end. Garnish with marjoram again if necessary.
If minute schnitzel is used, only cook it in the oven for 30 minutes without the lid.