In a small food processor combine the garlic, rosemary, preserved lemon, lemon juice, salt, and olive oil. Puree until everything is finely chopped. Alternatively, you can use a mortar and pestle to create a coarse paste.

Place the lamb on a work surface. Score the fat, being careful not to cut into the actual meat. (Translation: cut thin slits in the fat, about ¼ inch apart. This will help it melt away in the cooking process and allow the marinade to flavor the meat).

Rub the marinade all over the lamb, pressing it into the slits in the fat. Cover tightly in plastic wrap and chill in the fridge overnight.

Preheat the oven to 425 degrees F.

Remove the plastic from the lamb and set the leg, fat-side up, on a baking sheet or in a roasting pan. Cook for 15 minutes, then turn the heat down to 350 and roast for another 45 to 60 minutes, until the internal temperature is 130 - 135 degrees. Remove from the oven and rest for at least 20 minutes. Cut into thick slices and arrange on a platter. Serve warm or at room temperature.