Set up your grill for 2-zone cooking with a direct and an indirect heat area.
Season the steaks generously on both sides with salt and pepper. Allow the steak to sit for 5–10 minutes so that the salt can soak in a little.
Place your cast-iron pan in your grill over the direct-heat side. Place a small chunk of smoking wood directly on the coals (or make a woodchip packet to place on your burners)
Place the steak in the indirect zone and insert the probe from your DOT thermometer. Set the high-temp alarm on your DOT to 95°F (35°C). Close the grill lid (adjusting the position of your cast-iron pan if needed) and cook.
When your DOT's alarm sounds, open the grill and remove the probe from your steak.
Put 1 Tbsp butter in the skillet and melt it.
Set your timer for 30 seconds and put the steak in the pan. Start the timer.
When the 30 seconds have passed, flip the steak and restart the 30-second timer.
Flip after 30 seconds, then do it one more time.
Add the remaining butter and the herbs to the pan. Use a large spoon to baste the steak with the melted, herby butter for about 30 seconds, then flip the steak and continue to baste, checking the internal temperature frequently with your Thermapen ONE. (be sure to use a heat-proof glove or a hot pad to maneuver the pan handle … it was just in a grill!) Add the remaining butter and the herbs to the pan. Use a large spoon to baste the steak with the melted, herby butter for about 30 seconds, then flip the steak and continue to baste, checking the internal temperature frequently with your Thermapen ONE. (Be sure to use a heat-proof glove or a hot pad to maneuver the pan handle…it was just in a grill!) When you find a lowest internal temperature of 125°F (52°C)—for medium rare—remove the steaks to a platter to rest.
Serve, especially with grilled or speed-charred vegetables.