Set the sous vide to your desired temperature (132-degrees for medium-rare).
Vacuum seal the filet mignons using your preferred method. 2 steaks per bag.
Cook for 1 hour (for 1-inch thick steak), up to four hours.
Remove steaks and pat dry with paper towels. Season with salt and pepper.
Preheat a cast iron skillet over high heat. Add oil and butter. Sear steaks 1-minute per side, tilting skillet and spooning butter over them as they cook. Serve immediately.