Step 1Temper the steak: Remove the steak from the refrigerator and set aside to come to room temperature, 15 minutes or as needed. Blot the steak on all sides with paper towels to remove excess moisture. Season the steak on each side and along the edge with 1 to 2 teaspoons fleur de sel, or as desired. Liberally grind black pepper all over the steak.
Step 2Heat a cast-iron skillet over high heat until hot. Add 2 to 3 tablespoons oil to the pan, then quickly add the steak. Tilt the pan away from you, placing the steak in the pan away from the oil so it does not splatter. Do not move the steak in the pan, but rotate the pan to move the oil along the base of the pan, giving the steak time to develop a rich golden crust, about 3 minutes. Shortly before flipping the steak over, gently baste the top of the steak with spoonfuls of hot oil.
Step 3Carefully flip the steak in the pan. Continue to sauté on the other side, rotating the pan to move the oil while leaving the steak undisturbed as it forms a rich crust on the bottom, about 3 more minutes.
Step 4Check the steak for doneness. LeFevre prefers to cook the steak until the meat just begins to glisten as juices rise to the surface and the meat slowly springs back when gently pressed; a thermometer inserted into the thickest part of the steak should reach about 118 degrees (the temperature will continue to rise as it rests). Remove the steak to a cooling rack for 6 to 8 minutes to give the meat time to rest and recollect the juices before serving and slicing. Serve with a dipping bowl of creamy horseradish sauce.