Kitchen tip: If you can’t find small tenderloins, use one large (about 500 g). It will take 3 to 4 more min to reach 145F. Use a sharp fillet knife to remove the silver skin (sinewy membrane on the outside of the tenderloin). Pierce through a section of the skin with the knife flat against the surface of the tenderloin, then use long, even sliding motions to cut the skin off.