Mix first 5 ingredients in large glass baking dish. Season with generous amount of pepper. Add lamb, turning to coat. Cover and refrigerate overnight. Preheat oven to 450F. Drain lamb and transfer to large roasting pan. Season both sides with salt and generous amount of pepper. Arrange fat side down in pan. Roast 15 minutes. Reduce oven temperature to 375F and continue roasting until thermometer inserted in thickest part of lamb registers 130F for rare, about 20 minutes. Let stand 10 minutes. Cut into slices. Arrange on platter. Garnish with mint sprigs and serve. Serves 8. Bon Appetit March 1991