How to Cook Roast Lamb
To cook roast lamb, start by putting the lamb in a roasting pan. Then, brush it with olive oil and your favorite seasonings, like garlic, rosemary, and lemon zest. Once you've seasoned the lamb, add any vegetables you want to roast with it to the pan and put it in the oven. Cook the lamb for 30 minutes at 400 °F and then an additional 30 minutes at 350 °F. Once it's done cooking, let the lamb rest for 15 minutes before serving.
Preheat the oven to 400 °F (204 °C). It takes only a few minutes to prepare the roast for cooking, so preheat the oven before you get started. Place the leg of lamb in a roasting pan. Choose a metal, glass or ceramic pan that's just large enough to hold the entire leg of lamb. If you're roasting the lamb with vegetables, it's fine to use a slightly larger roasting pan. Rub the lamb with herbs, spices and oil. Place the garlic, rosemary leaves, salt, pepper, and lemon zest in a bowl. Pour in the olive oil and mix well. Rub the mixture all over the leg of lamb. If the mixture seems dry, add a bit more olive oil. You need enough of the rub to cover the entire leg of lamb. Make sure to cover the entire surface of the meat, so that each part cooks evenly and has great flavor. If you're roasting vegetables, add them to the roasting pan. Arrange them around the leg of lamb in a single layer, so that the vegetables cook evenly. As they cook, they'll absorb juices that run off the meat. Don't pile vegetables up the sides of the leg of lamb, since this may cause the lamb to cook unevenly. If you use russet potatoes, you might want to parboil them first to make sure they cook all the way through. Peel the potatoes and chop them coarsely. Bring a pot of water to a boil and boil the potatoes for 10 minutes, until they are halfway tender. Add them to the roasting pan when the meat is ready to cook. Roast the lamb for 30 minutes. Place the roasting pan in the oven and roast at a high temperature for half an hour. This will create a delicious crust around the leg of lamb. Reduce the heat to 350 °F (177 °C) and continue roasting. Roast for another hour at this lower temperature to make sure the meat gets cooked all the way through. Use a meat thermometer to check the internal temperature of the lamb and determine if it's ready. Leg of lamb tastes best when it's cooked between medium rare and medium well. For medium rare leg of lamb, remove the dish from the oven when the internal temperature has reached between 145 and 150 degrees Fahrenheit. For medium or medium well leg of lamb, remove the dish from the oven when the internal temperature has reached between 150 and 155 degrees Fahrenheit. Allow the lamb to rest for 15 minutes. Tent aluminum foil over the baking dish and let the lamb rest. This gives the juices time to reabsorb into the meat, creating a succulent, tender dish. After 15 minutes, you may carve the lamb. Whip up the mint sauce. Mix the mint, sugar, vinegar and water in a bowl. Use a whisk to whip the mixture until it's thoroughly incorporated. Arrange slices of roast lamb on a platter. Place the slices in an artful pattern on a single platter, or put a few pieces on the plates you'll be serving to people. Pour a little mint sauce over the lamb. Use a spoon to ladle a little sauce over the lamb slices. Its bright flavor provides the perfect contrast to the deep umami of leg of lamb. As an alternative, you may serve the lamb with some of the juices from the bottom of the pan, to keep the meat moist. Finished.  
Preheat the oven to 400 °F (204 °C). Place the leg of lamb in a roasting pan. Rub the lamb with herbs, spices and oil. If you're roasting vegetables, add them to the roasting pan. Roast the lamb for 30 minutes. Reduce the heat to 350 °F (177 °C) and continue roasting. Allow the lamb to rest for 15 minutes. Whip up the mint sauce. Arrange slices of roast lamb on a platter. Pour a little mint sauce over the lamb. Finished. 