Direction

1. Spread the lamb on a work surface. With a boning or paring knife, cut between the muscles and separate them using your fingers. Trim away any excess fat and gristle.
2. In a large, shallow dish, combine the olive oil, garlic, and rosemary. Add the lamb and turn to coat. Cover with plastic wrap; refrigerate at least 2 hours or up to 12 hours, turning a few times. Let stand at room temperature for 1 hour before grilling.
3. Preheat grill to high (450°F to 500°F).
4. Season the lamb with salt and pepper; do not scrape off the garlic or rosemary. Place lamb on oiled grates; grill, uncovered, turning often, until an instant-read thermometer inserted in each piece registers 125°F to 130°F for medium rare. The times will vary according to the size and shape of the lamb leg, anywhere from 8 minutes for a 6-ounce piece to 20 minutes for a 1 1/2-pound piece.
5. Transfer the lamb to a carving board as each one is done. Cover loosely with foil and let rest for 15 minutes. Thinly slice the lamb and serve.