Filet mignon is a steak cut of beef taken from the tenderloin which is the most tender cut of the beef. The Filet mignon can either be cut for roasts or for steaks. Beef tenderloin roast is sometimes labeled Châteaubriand, in honor of a noted French chef. Reserved for special occasions, due to being the most expensive cut of beef, the beef Filet mignon roast is a tender, juicy cut of meat. Filet mignon is best seasoned, seared, coating with mustard, and roasted to medium rare.