Pat lamb dry, and place, fat side up, on a rack in a roasting pan. Make several 1-inch-deep slits in lamb with a paring knife; rub olive oil mixture over lamb, pressing mixture into slits. Cover loosely with foil, and let stand at room temperature 30 minutes.
Meanwhile, preheat oven to 400°. Uncover lamb, and sprinkle with salt and pepper.
Bake at 400° for 2 hours and 30 minutes or until a meat thermometer inserted into thickest portion registers 145° (medium rare). Let stand 30 minutes before slicing.