Often used for roasts and stews, shoulder of lamb does best when cooked with a slow, moist heat. Cooked properly, the roast provides a rich taste and tender texture that warms the belly on cool evenings. When you get your lamb roast home from the supermarket or butcher's shop and prepare it for cooking, you may notice an opaque tissue covering the meat. Called a “fell,” this layering helps retain moisture within the roast and hold the shape of the meat -- do not remove it.
Preheat the oven to 160 degrees C (325F) and prepare your roasting pan by placing the roasting rack inside.
Rub the lamb with a light coating of olive oil and season with salt, pepper and spices of your choice. Lamb is very tasty on its own, so go easy on the spices, but complementary seasonings include fresh garlic, thyme, oregano and rosemary.
Place the lamb inside the roasting pan and surround it with the root vegetables. Put one the water or broth in the bottom of the pan. This helps get a good, moist heat going inside the pan and provides a liquid for basting and gravy.
Cover the roasting pan and place it on the middle rack of the oven. Cook for approximately 30 minutes per 450 g (1 lb). An average lamb roast weighs 1.3 to 1.8 kg (3 to 4 lbs) which means about a two-hour cooking time.
Baste the roast at the one-hour mark. Do not continuously lift the lid to check the roast, as this will prolong cooking time and let needed moisture escape. Baste on the hour and then every 20 minutes until the roast completes cooking.
Check the internal temperature of the meat by placing a meat thermometer probe into the thickest part of the roast. The lamb needs to cook to at least 63 degrees C (145F) for safe consumption. Cook to 70 degrees C (170F) for well done.
Remove the roast and allow it 10 minutes to rest before carving. This allows the meat’s juices to redistribute throughout the roast, making it easier to carve and more tender
Serve with the roasted root vegetables on the side.