With a tip of a small sharp knife, make slits all over the surface (about 15-20). Insert a sliver of garlic and a rosemary leaf cluster into each slit.
Rub the leg with olive oil, then generously season with salt on all sides.
Place the leg in a large, heavy-bottomed roasting or baking pan; cover and roast for 30 minutes.
Reduce the oven temperature to 350 degrees and continue to cook for 3-3.5 hours. (Check it to ensure the meat is tender. If not, cover and return to the oven.)
Remove cover, pour over with beer and bake for additional 30 minutes or until the top is browned.
Remove the roast and let it rest for about 20 minutes covered with aluminum foil. Keep in mind the temperature will increase a few degrees once it rests.
Cut most of the fat off from the meat so that the sauce doesn't get too greasy.
Lamb has a gamey aroma, but it's partially neutralized with garlic and rosemary. You can prep it the night before baking so that it marinates in the fridge. Beer helps even further, making the meat less robust.
Remove from the refrigerator at least an hour before roasting and allow it to reach room temperature. This way, you will avoid the "shock" that the meat experiences when you transfer it from the cold to a hot environment, and the roasted meat will have a nicer color.
During roasting, cover the pan with a lid or aluminum foil to concentrate all the flavors into the meat.
If necessary, pour a cup of water around the meat to prevent it from burning.
Add beer only during the last 30 minutes of baking the leg. Otherwise, the beer sauce will taste bitter. The alcohol will cook down, so this dish is safe for kids to consume.
Lamb is best cooked either short for a rare, pink, and juicy inside, or long and slow, so it's fork-tender. Anything in between can leave the meat tough and unappealing.
For the medium-rare, cook until a thermometer inserted into the thickest part, not touching the bone, reads between 135-145 F.
Check out additional information in the Ingredients Notes and FAQ section in the post.
Please keep in mind that nutritional information is a rough estimate and can vary significantly based on the products used and serving size.