I always buy topside,put beef in roasting tin and drizzle some oil over top,if no lid on roasting tin cover with foil,turn oven on high,when oven is realy hot put meat in and leave it for about ten mins,to seal the juices,then turn the oven down to half the temp,take out periodicly and baste you can add a little water to the juices if you wish,dont over cook when you think the meat is cooked,insert a skewer or sharp knife into the beef to make sure the juices run clear good luck