Ok, everyone likes their beef a certain way so here’s a general guide to getting it just the way you like it. Cook the beef for 15 minutes for every 450g for rare, adding another 15 minutes for medium rare and another 30 minutes for well done. For a 1.2 kg piece of rare beef, you’d need to cook it for 20 minutes at a high temperature then a further 55 minutes at 190C.