Preheat a water bath to 133°F using an immersion circulator.
Season flank steak with salt and pepper; place in vacuum bag. Add about a tablespoon of oil to the bag and massage to coat steak. Place herbs in the bag then seal.
Place the bag in the water bath and cook for 2 hours.
Remove steak from the bath and blot dry with paper towels
Heat a large skillet over high heat. Sear the steak until nicely browned on one side, turn over then add truffle butter to pan. Continue to sear the other side while tilting the pan and basting the steak with the melted butter.
Remove from pan, rest for about 3 minutes, then slice against the grain and serve with your favorite side dishes.