Cut the spring onions into fine rings. Cut the meat into 2-3 cm thick slices. Heat the oil in the pan. Fry the pork medallions on both sides over high heat, season with salt and pepper and remove. Add spring onions and sauté briefly. Add the cream, stock, crème fraiche and mustard and bring to the boil. Let the meat simmer in the sauce for 5 minutes. Season to taste with salt and pepper.