There's no need to thaw a frozen leg of lamb before cooking your Sunday roast. You can cook the lamb from frozen and save time in the process. However, when cooking a leg from frozen, you do need to add cooking time to make sure that the leg is cooked all the way through. Lamb goes well with herbs like rosemary and thyme and can be served for dinner or lunch. The time you need to cook the lamb varies based on the weight of the lamb.
Turn on the oven and preheat it to 180C. Take the lamb out of the freezer and place on a clean countertop.
Place the leg of lamb in a large roasting pan. Season with salt and pepper. Sprinkle the rosemary over the lamb. Leave the lamb out at room temperature for 30 minutes.
Place the lamb in the oven. To cook from frozen, add about a third extra to the cooking time. For example, if the usual cooking time is 60 minutes, add 20 minutes to the cooking time for a total of 80 minutes. For rare meat, cook the lamb for 37 to 40 minutes per 450 grams, 41 to 42 minutes per 450 grams for medium and 44 to 46 minutes per 450 grams for medium well. Use a meat thermometer to make sure the lamb is fully cooked. For rare, the lamb should reach 58C in the middle, for medium, the lamb should be 71C and for well done, 80C.
Take the roast out and cover with aluminium foil. Let it sit for 10 minutes.
Carve the lamb with a sharp knife and serve on to warm plates.
Never serve lamb that is red and bloody in the middle. If necessary, pop the joint back into a hot oven for 15 minutes.