Grilled Leg of Lamb with Rosemary, Garlic, and Mustard

1 well-trimmed 6-pound boneless leg of lamb, butterflied to even 2-inch thickness

8 garlic cloves, peeled, divided

1/2 cup whole grain Dijon mustard

1/2 cup extra-virgin olive oil

1/4 cup dry white wine

2 tablespoons finely chopped fresh rosemary

2 tablespoons fresh lemon juice

Nonstick vegetable oil spray

Fresh rosemary sprigs and fresh Italian parsley sprigs

Open lamb like book on work surface. Using tip of small knife, make 1/2-inch-deep slits all over lamb. Thinly slice 4 garlic cloves. Insert garlic slices into slits in lamb. Combine remaining 4 garlic cloves, mustard, olive oil, white wine, rosemary, and lemon juice in processor. Blend until coarse puree forms. Spread underside of lamb with half of puree. Place lamb, seasoned side down, in 15 x 10 x 2-inch glass baking dish. Spread remaining puree over top of lamb. Cover lamb with plastic wrap and chill overnight.

Let lamb stand at room temperature 2 hours. Coat grill rack with nonstick spray and prepare barbecue (medium-high heat). Sprinkle lamb generously with salt and pepper on both sides. Grill lamb to desired doneness, about 17 minutes per side for medium-rare. Transfer lamb to cutting board; let rest 10 to 20 minutes.

Thinly slice lamb against grain. Overlap slices on platter. Sprinkle with salt and pepper. Garnish with fresh herb sprigs.