Lay 12×12-inch square of plastic wrap on counter. Place 1/3 of salt mixture in center of plastic wrap; lay beef tenderloin on top. Place remaining salt mixture on top and sides of beef tenderloin, pressing to cover completely. Pull the plastic wrap tightly around the beef and seal. Place beef in zipper-topped plastic bag; seal. Place beef in refrigerator and cure for 24 hours, turning over every 8 hours. Remove beef tenderloin from plastic wrap; brush off all salt mixture. Slice beef thinly.
