Sear the meat for about 2-3 minutes in hot oil (I prefer rapeseed oil) and keep warm in aluminum foil. Reduce the heat and fry the onions cut into strips until translucent (add a little oil if necessary).
Deglaze the roast set and onions with a little water and stir in the sour cream and the two types of mustard. Salt and pepper the meat and put back in the pan. Let it heat up briefly and season with paprika powder, salt and pepper.
Finally stir in the finely chopped parsley.
If the sauce is too thick, just add a little broth (instant).