De-bone and trim the leg well or have your butcher do it. Smash the garlic cloves and mix with the rosemary, thyme sprigs, and cracked pepper. Add 1/2 cup of olive oil and rub all over the meat. Marinate, covered, in the refrigerator, for 1 to 2 days. Remove the herb sprigs and garlic cloves from the meat.
Preheat the oven to 400 degrees F. Mix the chopped garlic, rosemary, and thyme with enough olive oil to dampen into an almost paste-like consistency. Add salt and pepper, to taste.
Season the lamb well with salt and pepper. Spread the interior liberally with tapenade. Roll up and tie with string. Heat a large saute pan over medium-high heat. Add 2 tablespoons of olive oil and place the lamb in the pan, fat-side down. Sear until golden and turn over so that all sides are seared. Place fat side up in the pan and use a large fork to hold the lamb while you drain off any excess fat.
Pat the chopped herbed mixture all over the outside of the lamb. Add 2 cups of water to the pan and roast for 1 1/2 hours until a meat thermometer reads 125 degrees F. Let the meat rest for 15 minutes before slicing. Slice thinly and serve with roasted potatoes. Serve extra tapenade on the side or pan juices.
Place all the ingredients except the olive oil and the parsley in a food processor. Chop coarsely by pulsing the machine. Drizzle in the olive oil and pulse a few more times, season with salt and pepper. Fold in the parsley by hand. The tapenade is best when made a day in advance so flavors have time to marry.
Recipe courtesy of Maria Helm Sinskey, Robert Sinskey Vineyards