Get top rump of beef and rub the lean parts with salt & pepper and the fat with flour and dry mustard(Colmans). 1lb to 1 1/2 lbs of beef is plenty for 2 with enough to have cold the next day!
Preheat the oven to 230degC and cook for 20 minutes.
Then turn heat down to 190degC and continue to roast, basting at least 3 times, for 15 minutes per pound for rare, plus a further 15 minutes for medium and another 30 minutes for well done. Rest for 20-30 minutes before carving.
I found that medium is best and the coating and high starting temperature really seals in all the flavour!