Peel and dice the potatoes. Clean the leek and cut into rings (approx. 1/2 cm). Heat some oil and fry both briefly in it.
Deglaze with the hot meat stock and bring to the boil. Cover and let stand over low heat for about 10 minutes.
Clean the Kassler, dice it and add it to the vegetables. Season everything with marjoram, mustard, salt and pepper and cook for another 10 minutes with the pot closed.