This is a classic lamb dish. Rosemary, garlic and mustard pair very well with lamb and are natural flavor enhancers. I like to serve lamb for special occasion meals like Rosh Hashannah or Succot. I serve it with flowered roasted potatoes. This dish is grilled but an indoor grill pan works well too.
1 well-trimmed 4-pound piece of lamb, butterflied to even 2-inch thickness (ask the butcher to butterfly it for you).
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 15x10x2-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) or grill pan. 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.