To a small mixing bowl, add the olive oil, Dijon mustard, soy sauce, thyme, rosemary, garlic powder, and pepper. Mix well.

Rub the mixture evenly over the beef tenderloin, making sure it’s coated evenly.

Place the beef tenderloin in a vacuum-seal bag or a large Ziploc bag (I recommend using a Ziploc heavy-duty freezer bag, and I don’t recommend using an off-brand because of the thickness of the bag and the strength of the seams). Remove as much air as possible, and seal. (See notes for the water displacement method if you’re using a Ziploc bag.*)

Fill a large pot with 5-6 inches of water. Place your sous vide machine in the water, attaching it to the side of the pot. Preheat your sous vide machine to 133°F for medium-rare or 140°F for medium (my personal favorite). Adjust the temperature based on your desired level of doneness.

Submerge the sealed beef tenderloin in the sous vide bath, making sure the beef is fully underwater, and clip it to the side of the pot. Cook for 2 hours. Don’t cook it for longer than 3 hours, or it will start to get mushy.

Once cooked, remove the beef from the bag.

In a cast iron skillet over medium-high heat, melt the unsalted butter. Once it starts foaming, add the minced garlic. Saute until the garlic is fragrant, about a minute, stirring frequently to prevent the garlic from burning.

Place the beef tenderloin into the skillet. Sear for about 60 seconds on each side, continuously spooning the garlic butter over the beef to baste it while searing.

Remove the beef from the skillet and let it rest for about 10 minutes before slicing.