1Combine the first 7 ingredients in a small bowl; stir well.
2Place the tenderloin in a large shallow dish; pour the marinade mixture over the tenderloin. Cover and marinate in the refrigerator 8 hours, turning occasionally.
3Remove the tenderloin from the marinade, reserving the marinade. Place the marinade in a small saucepan. Bring to a boil; reduce heat, and simmer 3 minutes. Set aside.
4Place the tenderloin on a rack in a shallow roasting pan; insert a meat thermometer, making sure it does not touch any fat. Bake at 425 degrees for 45 to 55 minutes, or until the thermometer registers 140 degrees (for rare), 150 degrees (for medium-rare), or 160 degrees (for medium). I do not suggest you cook this more than medium rare for best flavor and tenderness. Baste occasionally with the marinade. Let the tenderloin stand 10 minutes before serving.
5Saute the mushrooms in 1 tablespoon melted butter in a skillet until tender; set aside, and keep warm.
6Place any remaining marinade in a small saucepan; add water and 2 tablespoons butter. Bring to a boil; reduce heat, and simmer 3 minutes. Slice tenderloin; spoon sauce over tenderloin. Top with sauteed mushrooms.