serves 4 to 6
1 head garlic, about 10 to 12 cloves, peeled
4 large sprigs rosemary, leaves removed
zest of 1 lemon
Freshly ground black pepper
1/4 cup extra virgin olive oil
3 1/2 to 4 pounds bone-in leg of lamb, preferably tied and fat scored
Place garlic cloves in a food processor fitted with a steel blade. Pulse until well minced. Scrape down sides of processor bowl with a rubber spatula. Add rosemary, lemon zest, 2 tablespoons salt and 2 teaspoons pepper and pulse until rosemary is well chopped and a thick paste forms. Scrape down sides of bowl down, again. With machine running add olive oil in a steady stream and process until combined.
Place lamb in a roasting pan and pat it dry with paper towels. Cover leg entirely with the garlic and rosemary mixture. Refrigerate, uncovered, for 8 hours or overnight.
Take lamb out of refrigerator to come to room temperature 1 hour before roasting. Preheat oven to 375 F.
Roast lamb until an instant read thermometer inserted in the thickest part of the leg reads 125 F for medium rare, about 50 minutes to 1 hour and 5 minutes, or up to 1 hour 20 minutes for medium at 135 F.
Transfer lamb to a cutting board to rest for 20 to 30 minutes. Carve lamb into 1/2-inch thick slices, reserving any juices from the cutting board, and serve.