Peel the potatoes, wash the leek and cut both into small pieces. Heat the oil and sear the meat all over. Remove. Briefly fry the leek and potatoes in the remaining oil and season with salt and pepper. Pour in hot water and stir in the stock cube. Simmer for approx. 15 minutes. Stir in the parmesan and processed cheese and continue to cook until the potatoes are al dente. Add the meat and parsley. Flavour with salt, pepper and horseradish.