Preheat the oven to 220C.
Using a pestle and mortar coarsely grind the peppercorns. Sprinkle these onto a chopping board or a flat plate.
Using a silicon brush smear the mustard over the beef then roll the beef in the peppercorn.
Heat a Tbsp of oil in a frying pan until very hot. Sear the beef for about 3-5 minutes, turning regularly.
Put the beef in a roasting tray and put it in the oven for 15 minutes.
Turn down the oven to 180°C and cook for a further 15-30 minutes, depending on how well cooked through you like your beef.
Rest the beef for 15 minutes (covered) before carving. In the meantime make some gravy from the cooking juices.