Verified answer

I have cooked(roasted) many legs of frozen lamb,and very nice they are too.I have always defrosted them first.It would not occur to me to cook it frozen.To cook from frozen would possibly be a health risk as parts could be uncooked and prone to bacteria I would think.To defrost I would put the leg,unwrapped in a tray or dish in my microwave oven(did not switch it on) overnight and the next morning would rinse under a cold tap,dry with a kitchen towel,place in a roasting tin,sprinkle with oil and add rosemary .Place in a preheated oven on a middle shelf and cook at a high setting for about 20 minutes,Turn the heat down to about Gas 5 or 6 for the remainder of the time.(The weight of the joint would determine the total cooking time and how well done you like it).

Yes you can. There is no food safety risk as bacteria need four things to grow - moisture, oxygen, time and temperature. As you are taking away the time factor as in cooking it as it defrosts it will not have time to grow bacteria. Cooking from frozen can be achieved easily if you cook at a lower temperature say 140 degrees Celsius until meat is defrosted then slowly bring the temp up to 180 degrees Celsius. If you account for the longer cooking time because it's frozen you should have a reasonable quality leg. You have more risk of getting sick by defrosting in a microwave overnight because you give the lamb time to grow bacteria in an uncontrolled environment ie warm.

If you cook a piece of meat frozen, it turns out very nasty. It gets dry as cardboard. The outside is over done and the inside is under done.

Defrost it first before you roast it.