In a small bowl, combine the first five ingredients. Pour half of the marinade into a large resealable plastic bag. Pierce tenderloin in several places; add to the bag and turn to coat. Seal and refrigerate for 8 hours or overnight. Cover and refrigerate remaining marinade for basting.
Place potatoes in a large saucepan and cover with water. Bring to a boil; cook for 15-20 minutes or until crisp-tender. Drain; toss with butter, salt and pepper.
Drain and discard marinade. Place tenderloin on a rack in a shallow roasting pan. Arrange potatoes around meat.
Bake, uncovered, at 375° for 60-75 minutes or until beef reaches desired doneness (for medium-rare, a meat thermometer should read 145°; medium, 160°; well-done, 170°), basting occasionally with reserved marinade. Let stand for 10 minutes before slicing; serve with pan juices and potatoes. Yield: 10-12 servings.