Combine first 4 ingredients, stir well. Spread mustard mixture over meaty portion of lamb racks; set aside. Combine the milled nuts with 1/4 teaspoon salt, pepper, butter, and bread crumbs. Pat mixture over mustard-coated lamb. Place roasts on a rack in a roasting pan, fat side out and ribs crisscrossed. Insert meat thermometer into thickest part of lamb, making sure it does not touch bone. Roast at 180° for 20 minutes or until thermometer registers 60° (medium). (Cover roasts loosely with foil after 25 minutes if necessary to prevent excessive browning.) Let stand 10 minutes before slicing. When you’re preparing racks of lamb, let a butcher do some of the work for you. Ask him to french the chine bones (remove fat and gristle) and to trim the cap fat, leaving only the tender eye meat and resulting in a beautiful entrée presentation. Reduce port wine and veal broth for about 20 minutes, until thicker consistency. Add in the butter.