One should have as little gray band as possible when searing a steak. This is the fully cooked meat below the crust of a seared or grilled steak and above the undercooked center.
To minimize the gray band, start with a frozen steak. The heat cannot penetrate as deeply in a frozen one, so the interior is cooked as little as possible while the crust develops.
You need a thick steak, frozen flat with little trapped moisture. Wrapping the steak before freezing will just trap more moisture, so keep it unwrapped.
Once frozen, sear the steak in a cast iron skillet with a high smoke point oil until it crusts. Season it with salt and pepper, then place it in a low-temperature oven until done.
Let it rest for 10 minutes before carving to preserve its juiciness. For a touch of extra flavor, accompany the steak with compound butter.
Another method to minimize the gray band is a so-called reverse sear. The steak is cooked in a controlled temperature using a sous vide machine, then is seared to develop a crust.