In a small bowl, combine garlic, rosemary, and pepper. Add olive oil and lemon juice. Mix until all ingredients are combined.
Remember - Do not remove the netting that is around the lamb roast.
Rub the Herb Seasoning Rub mixture all over the outside of the lamb.
Room Temperature: To cook evenly, the lamb roast must not be cold - let it stand at room temperature, loosely covered, for approximately 1 hour or even more. This time can vary depending on how big or small your lamb roast is. I can not give you an exact time on this. If you do not let the roast come to room temperature, it will take longer to cook your roast. Your roast will not cook evenly, and you will end up with well-done slices on the end and raw meat in the center. Use your best judgment!
Previously Frozen: If your boneless leg of lamb is frozen, let it thaw completely in the refrigerator. Remove the roast from the refrigerator about 2 to 4 hours before cooking to let it come to room temperature. Depending on the size of your roast, the time to come to room temperature may vary. I can not give you an exact time on this. Use your best judgment!
Preheat oven to 450 degrees F.
Pat the room-temperature boneless leg of lamb roast dry with paper towels or napkins. Using your hands, rub the outside of the lamb roast with olive oil or with the Herb Seasoning Rub (see above Herb Seasoning Rub).
Do NOT salt the outside of your lamb roast, as salt draws out moisture from the meat while cooking. You can use other seasonings or the Herb Seasoning, if desired, but I find it is not necessary. I know that some people do salt their meats before cooking, but trust me and do not salt - the result will be a juicy and delicious lamb roast to serve your family and guests!
Place the lamb roast on a roasting rack in a heavy stainless-steel pan or other metal roasting pan. NOTE: Select a roasting pan that has sides at least 3-inches deep. (I do not recommend using nonstick pans, as these pans yield fewer of the cooked-on bits that make the tasty au jus juice.)
Sear the lamb roast for 15 minutes at the higher oven temperature (450 degrees F.), then turn the oven to the lower temperature (325 degrees F.) for the rest of the cooking time. Do Not Cover the roast.
NOTE: If you ignore every other bit of advice I have given, please pay attention to this - For a perfectly cooked leg of lamb roast, invest in a good meat thermometer. Internal temperature, not time, is the best test for doneness and you don't want to blow this meal!
Insert meat thermometer so tip is in thickest part of lamb (not resting in fat). Cook until the lamb roast reaches an internal temperature of 120 degrees F. Remove from oven, cover with aluminum foil, and let sit approximately 15 to 20 minutes. Remember, the lamb roast will continue to cook as it sets. The temperature will rise to 125 degrees F. to 130 degrees F. internal temperature (medium rare) at 15 to 20 minutes. If allowed to rest as long as an hour, the temperature will rise even higher. So, pay attention to how long you let the cooked lamb roast sit.
About 1/2 hour before the estimated end of the roasting time, begin checking the internal temperature.
Place the cooked lamb roast on a large Meat Cutting Board with a well at one end to hold the juice.
Using your scissors, cut off the netting to remove and discard it. Using a sharp knife, slice the meat across the grain into whatever thickness you prefer. Sharpen your Carving Knife, if necessary using either a sharpening rod or stone.
Steel Sharpening Rod: To use a Steel Sharpening Rod or Steel, pull the edge down and across the rod, holding the carving knife at the same angle. Do this anywhere from 5 to 10 times.
Sharpening Stone (whetstones): To use a Sharpening Stone (whetstones), hold the carving knife at a 10 to 15-degree angle to the stone. Push back and forth in smooth, steady strokes.
Au Jus is aFrench term meaning "with juice." The term is used to describe the serving of meat, most often prime rib roast, but this technique works great with Leg of Lamb, surrounded in or served with a container of the natural juices that were produced as drippings while the meat was being cooked. It is not thick like a typical sauce or gravy.
While the cooked lamb roast is resting, now is the time to make a sauce from the drippings. Carefully spoon off any excess fat and discard. Scrape the bottom of the roasting pan to loosen the sediment. Pour the lamb juices (from the bottom of the roasting pan) into a saucepan. Add some red wine and some of the herbs (if used) that are left in the roasting pan.
IMPORTANT: Making Au Jus is more of a technique and not a recipe. You will have to do this by feel or guess work. It depends on how much juice is left in your pan (plus the juice from slicing the lamb roast), and how many people you will be serving.
Add the wine to the saucepan with the lamb juices and bring to a boil, and cook until the stock is slightly reduced, about 5 minutes. NOTE: Au jus is not thick like a typical sauce or gravy. Add the butter and mix it in by swirling the pan. Season to taste with salt and pepper. Transfer to a gravy boat.
Serve this sauce on the side when serving the sliced lamb roast. NOTE: Some chefs will strain the sauce before adding the butter (your choice).
* Add your wine according to how much Au Jus you think you will need for each person being served. I wish I could give you exact directions, but it is impossible to have an exact recipe for this. I usually use the same style of wine in the au jus that I will be serving at the dinner.
Perfect Boneless Leg Of Lamb Roast Recipe: https://whatscookingamerica.net/Lamb/Roast_Boneless-LegLamb.htm