Heat a liter of water with salt and sugar. Add spices (Kaffir lime leaves are great). In a cold marinade, place the meat and leave for at least an hour at room temperature, and preferably overnight in the refrigerator.
Shake the meat from the marinade, put it in the bag with the spices. If it is not marinated for long, add large sea salt. Close the package using a vacuum sealer – or put the tenderloin in a package with a zip, immerse the package in a pan with cold water and close the lock when it is 3 mm above the water surface.
Pour water into a sous-vide or multicooker, set the temperature to 60 degrees and time: one and a half hours. Put the sealed bag into the water, press the Start button.
After one and a half hours, the tenderloin, which has preserved juiciness and pink color, can be carried to the table. If you like a ruddy crust, you can quickly fry the meat in a hot frying pan.