Start by heating your sous vide to 52 degrees Celsius or whatever temperature you find best.
Then trim your tenderloin. Remove any tendons or other rough pieces that you see on the meat. The tendons usually have a different kind of slight blue and green shimmer to it. The tendons will never be tender no matter how long you cook it, therefore you should cut it off.
Rub the tenderloin with salt and pepper.
Fold the top of the sous vide bag down and add the loin and a bit of oil.
Vacum the bag and drop it into the water for 1 hour 30 minutes.
Heat up the pan (grill or woodfierd oven) until its blistering hot.
Remove the loin from the sous vide bag and drop it into the pan with a bit of oil.
Sear the steak until it gets a crisp brown crust. It is important that this the pan is hot enough so that you get a good crust before the meat gets over cooked.
After searing wrap the loin in tinfoil and let it rest for 50-10 minutes before you cut it.
Slice the loin into 1 cm slices and spread chimichurri over.