Heat a cast iron skillet to medium high and add in the oil and butter. Add salt and pepper to both sides of the steak, then sear for 2 minutes on each side, and resist the urge to move them before then. You want to get a nice sear and avoid them sticking to the pan.
Quickly sear each side of the steaks, then place the steaks in the skillet in the oven and cook for 5-7 minutes for medium rare. I pulled mine out at 125°F on a meat thermometer, and allowed it to rest before cutting into it.
The temperature can increase by about 5°-10°F from the residual heat as it's resting. If you cut into it (or any meat) too soon, without allowing it to rest, you run the risk of the juices running out, instead of redistributing. So do not skip this step, the wait will be well worth it, I promise!
As the steaks are resting, you can add a disc of the optional Garlic Herb Compound Butter over the tops so it can slowly start to melt. Or you can top with a pad of regular butter instead.
Cooking times will vary according to how you like your steak:
4-5 minutes for rare
5-7 minutes for medium rare
6-7 minutes for medium
8-9 minutes for medium well
12-14 minutes for well done
*See post notes for the rate temperatures/doneness cooking chart.