Preheat the oven to 200C/400F/Gas 6.
Season the steak, to taste, with salt and freshly ground black pepper.
Heat the oil and butter in an ovenproof frying pan. When the butter is foaming, fry the steak for 3-4 minutes on each side, or until browned on both sides.
Transfer to the oven and cook for a further 5-10 minutes (for medium), or until cooked to your liking.
Serve garnished with chopped chervil.
