Preheat your sous vide water bath to your desired doneness level. Refer to the time and temperature chart below.
Use salt and pepper to season the pork tenderloin. Chop or slice your garlic and shallots, then distribute evenly together with half of the herbs throughout the sous vide bag. Place your meat in the bag and seal airtight.
By this time, the water bath should be at the desired temperature. Place your prepared sous vide bag (with the meat and herbs inside) into the water bath for the time recommended in the chart below.
Once it’s fully cooked, remove your meat from the container and bag. Check the internal temperature to make sure it’s 145ºF to be safe to consume.
Prepare a paper towel and carefully pat your pork tenderloin dry. Heat up your olive oil in a cast iron skillet on your stove, until the oil starts to lightly smoke.
Place your pork in the skillet using a pair of tongs, turning every 30 seconds. A total cook time of 2 minutes should be enough for a good sear without drying out the insides.
Add your butter, and the other half of your herbs, garlic and shallot for extra flavor. Cook everything in the pan for about 30 seconds, tilting the pan every so often and using a spoon to baste your pork with the herb butter, simple sauce in the large skillet.
Take your pork out of the skillet and place it on a rack on top of a tray lined with a baking sheet.
Reserve all the drippings left in the heavy skillet and pour it on top of your pork.
Let it rest for 2 minutes – then slice it up and serve.