From the lamb people:

Serves 8
Perperation time: 15 min (took me a couple hours)
Marinagte time: 4 hrs to overnight (overnight of course)
Cook time: 40 - 50 min (took 2+ hours)

1 tablespoon dry mustard
1 teaspoon ground cardamom (may substitue ground ginger)
1 tablespoon apple cider vinegar
1/2 cup frozen apple juice concentrate, thawed
1/2 cup dijon mustard
1 tablespoon fresh rosemary
2 tablespoons olive oil
Coarse kosher salt
4 to 6 lbs American Lamb leg, boned and butterflied

Combine first 3 indredients in small bowl. Gradually whisk in vinegar. Let stand 15 minutes. Whisk in apple juice concentrate, mustard, rosemary, and oil. Season marindade to taste with coarse salt and pepper.

Place lamb in glass baking dish. Spinkle with salt and pepper. Spread 1/3 cup of marinade over the top to coat. Turn over. Sprinkle with salt and pepper. Spread remaining marinade over lamb. Cover dish with plastic wrap and cill overnight.

Preheat grill to medium heat and spray grill rack with nonstick spray. Place lamb on grill and reserve dish with marinade. Grill 15 minutes. Turn lamb over. Grill 15 minutes, brushing with marinade from reserved dish. Turn lamb over again and grill untill thermometer registers 145 for medium-rare, 160 for medum or 170 for well. bursh often with marinade. Cover loosely with foil and let rest 15 min. Slice lamb thinly and arrange on platter to serve.