Step 1

On a cutting board, coarsely chop the crushed garlic. Sprinkle with the salt and then finely chop and, using the flat side of the knife, smear the garlic and salt into a coarse paste.

Step 2

Add the rosemary and lemon zest and continue chopping and scraping until well combined. Scoop into a small bowl and stir in the oil, lemon juice, and pepper to make a thin paste. (Alternatively, you can purée all of the ingredients in a mini food processor.)

Step 3

Place the lamb on a large rimmed baking sheet. Using the tip of a small sharp knife, pierce the lamb about 15 times, making slits about 1 inch (25 mm) wide and deep all over the lamb.

Step 4

Using a small spoon and your fingertips, fill each slit with some of the rosemary paste. Slather the remaining rosemary paste all over the lamb. Cover with plastic wrap and refrigerate for at least 4 hours or overnight. Remove from the refrigerator and let stand at room temperature for 1 hour to remove its chill before cooking.

Step 5

Position a rack in the bottom third of the oven and preheat the oven to 400°F (200°C).

Step 6

Place the lamb in a large roasting pan and roast for 15 minutes.

Step 7

Reduce the oven temperature to 350°F (177°C). Continue roasting until an instant-read thermometer inserted in the thickest part of the lamb (not touching a bone) reads 130°F (55°C) for medium rare, about 1 1/4 hours. During the last 20 minutes of roasting, arrange the lemon slices on top of the lamb.

Step 8

Move the lamb to a carving board and let rest for 10 to 15 minutes. Set the lemon slices aside.

Step 9

Using the leg bone as a handle, carve the lamb by slicing vertically along the roast in the boneless area, then parallel to the bone in the shank section.

Step 10

Arrange the slices on a platter and pour the carving juices on top. Garnish with the rosemary sprigs and lemon slices and serve.