Season the steak liberally with salt. Place the steak, garlic and lemon thyme in a vacuum-sealed container.
Cook in a 140-degree Fahrenheit (60-degree Celsius) water bath for 55 minutes to reach medium-rare stage.
Remove the steak from the vacuum-sealed container, and discard the sprig and garlic. In a heavy-bottomed pan, set to medium-high heat and pan sear the steak so each side is nicely browned. Place the butter in the pan and let melt. Cook another 30 seconds.
Allow the steak to rest for 3 minutes. Sprinkle with pepper and serve.