Preheat oven to 400°F.
Heat oil in an ovenproof skillet over medium-high heat. Generously season tenderloin with salt and pepper. Sear in oil until well-browned on all sides, about 10 minutes. Place in oven and cook to medium-rare, about 15 minutes or until a meat thermometer reads an internal temperature of 140°F.
Preheat your Precision Cooker to 131.5°F. Allow the water bath to come ot temperature before adding your steak.
Season the steak generously with salt and pepper and then slide it into a vacuum-seal or heavy-duty zipper lock plastic bag.
Drop the bag in the water bath, making sure not to block the intake or output of your Precision Cooker. If properly sealed, the steak should sink. Cook for 45 minutes.
Remove the seak from the bag and palce it on a paper towel-lined plate. Pat it dry very carefully on both sides.
Turn on your exhaust and open windows. Place a heavy cast iron or stainless steel skillet on high heat with 1 tbsp of vegetable oil. Gently lay the steak in the skillet using tongs. After 15 to 30 seconds, flip the steak. Repeat flipping the steak until it has a nice brown sea - about a minute and a half in total.
Recipe adapted from: Wilson-Vuksanovic, Tania. "Thai Beef and Mango Salad on Rice Noodles." Food & Drink. Winter 2008.