If you want to serve the roast meat of old England for a special occasion, it’s best to get as large a joint as possible. The perfect roast includes a lovely crusty outside and lots of tender, succulent meat within. My advice is to buy a decent-sized piece of sirloin for a special occasion, and otherwise a double rib joint (which as it happens is next door, anatomically). When you buy a piece of sirloin, make sure it contains the eye or undercut, which some butchers take out and sell as fillet steak (which it is). A decent joint of sirloin on the bone will weigh 4-5 lb (2-2.5 kg). If you are worried that your family is too small to cope with a large joint, bear in mind that good roast beef is delicious cold with chutney and jacket potatoes, and minced it makes lovely cottage pie.
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