Kosher salt and freshly ground black pepper, to taste
2 thyme sprigs
1 garlic clove, smashed
1 (4-inch) rosemary sprig
1 (3-inch) piece lemon zest
2 tablespoons vegetable oil
1 tablespoon unsalted butter
Flaky sea salt, for garnish
Directions
Season the steak liberally with salt and pepper.
Place steak in a vacuum-seal bag with the thyme, garlic, rosemary, and lemon and vacuum seal closed. Alternatively, place the ingredients in a sealable plastic bag and dip the bag into a large bowl of water to displace the air before sealing shut.
Preheat a pot of water fitted with a sous-vide immersion circulator to 129 F according to the manufacturer's directions.
Cook the steak for 2 hours, making sure it is completely submerged in the water.
Remove the bag from the pot and take the steak out of the bag, drying with paper towels.
In a large cast-iron skillet, heat the vegetable oil over high heat. Add the steak and cook, flipping once until seared on both sides, about 1 minute per side.
Add the butter and baste the steak for 10 to 15 seconds more. Transfer to a board to rest for 5 minutes.
Slice the steak and garnish with flaky sea salt, then serve.