Once the potato has finished baking (you should be able to easily slide a knife through the center without resistance) remove it from the oven, carefully cut it in half, and set it on a cutting board or plate to cool down. It will take some time, so don't start cooking the steak until this has happened.
Preheat the cast iron pan on medium high heat then add 1 tablespoon olive oil and swirl gently to coat the bottom of the pan.
Season the steak with fresh cracked pepper and when the oil just starts smoking add the steak to the pan making sure to lay it away from you to prevent oil from splashing towards you.
Turn the heat down to medium and use tongs or a large spoon to press the steak flat against the pan. Do not touch the steak for at least 4-5 minutes to allow it to establish a sear on this side.
Flip the steak and add 1 tablespoon of unsalted butter to the pan. Once it melts completely, gently tilt the pan to the side and use a spoon to baste the steak with the melted butter.
Lay the pan flat and use tongs or a large spoon to keep the steak pressed against the pan. Allow the steak to cook for 4-5 minutes, basting the steak at least every minute.
Use an instant read thermometer to check the internal temperature of the steak OR press the thickest part of the steak to check for doneness. The thermometer will always be accurate, pressing the steak can be learned with experience.
If the steak is not cooked to your desired temperature, flip it and cook for another two minutes basting regularly. Test again for doneness. Repeat until steak is cooked to the desired temperature then remove from the heat.
Set the steak on a plate loosely covered with aluminum foil to rest while you finish the potato.