Combine first 8 ingredients, mixing well. Set aside.
Place lamb, fat side down, in bottom of shallow roasting pan. Bake at 500° for 8 minutes or until golden brown. Remove from oven, and place lamb, fat side up, in roasting pan.
Combine mustard and rosemary; brush on lamb. Cover lamb with breadcrumb mixture; insert meat thermometer in one of the racks, making sure it does not touch fat or bone.
Reduce heat to 300°; bake lamb until meat thermometer registers 140° (rare), 160° (medium), or 170° (well done).