Cut the meat into pieces approx. 3 cm wide. Heat 1 tablespoon of clarified butter in a pan and fry the fillet slices for 3 - 4 minutes on both sides. Season to taste with salt and pepper and then set aside.
Dice the onion and fry for 1 minute with the remaining clarified butter. Add the mushrooms and fry vigorously for about 5 minutes. Deglaze with white wine and reduce to a creamy consistency with the stock and cream. Add salt, pepper and parsley. Heat the fillet slices in the sauce for another 3 minutes.
This goes well with croquettes, potatoes or spaetzle.