Rub the salt all over the pork tenderloins and let them sit, uncovered, in the fridge overnight.
Heat a sous vide water bath to 134F degrees for rare or medium-rare (see table above for more options).
Combine the remaining ingredients in a bowl and mix well to combine.
Place the pork in a vacuum sealable bag (or ziplock freezer bag if using the water displacement method above) and pour the liquid over the top.
Use the moist setting on the vacuum sealer to seal.
Place in the water bath and cook for 2-4 hours.
Remove from bag (reserving the bag juices) and place in an ice bath for 5 minutes to stop the cooking process (this helps to not overcook when searing it).
Heat a cast iron skillet on high heat until almost smoking. Add 1 tablespoon of avocado oil (or any high smoke point oil).
Sear the pork tenderloins for 45-60 seconds per side, until a brown crust has formed (be very careful not to overcook here).
Remove from the pan and let cool for 5 minutes. Slice and serve with reserved bag juice.
Removing the air from the bag is an important step that should not be skipped to avoid bacteria entering the bag.
The pork tenderloins may float in the water bath. For even cooking, they should be completely submerged. To prevent floating, you can way the bag down with something heavy like a wet towel or thissous vide sinker weight.
If air gets in the bag, just open the bag, let the air out and reseal it.
For the best crust, use some paper towels to pat the pork dry before placing it in the hot skillet.
The skillet should be extremely hot before adding the pork so it sears quickly without overcooking.
Don't sear the pork tenderloins for more than 45-60 seconds per side as they will overcook.
Omit the sherry in the sauce if you prefer and just substitute with vegetable or chicken stock.
If you find your pork tenderloins turn out a little tough, try removing the silver skin. This is a thin membrane often found on the surface of pork tenderloins. It can get tough when cooked.