Fry the medallions on both sides for 4 minutes. Keep warm in the preheated oven (150 ° C). Switch off the oven. Braise the onion in the meat stock, deglaze with the stock. Add the cream and sour cream. Let everything simmer. Season with the mustard and a lot of pepper. Fold in the cream cheese and thicken with the cream sauce. Boil the pasta and toss in a little butter.