Preheat the oven to 375*. Let the steak come to room temp. Heat a cast-iron skillet over medium-high heat for 5 minutes. Meanwhile, rub butter over both sides of the steak. Generously rub steak with seasoning. If needed, cut the steak into chunks so it will fit in the pan.
Add the grapeseed oil to the skillet. Substitute olive oil if no grapeseed oil is available, I like to use grapeseed oil for its high smoke point. Just make sure to have the exhaust fan on high. Place steak into the cast iron skillet and cook for 2 minutes per side. Turn off the heat.
Place cast iron into the oven for 5 minutes for rare, 6 minutes for medium rare, or 7 minutes for medium. Check temp with a meat thermometer, Steak will rise 5 degrees as it rests. (Remove at 120* for rare, 130* for medium rare, and 140* for medium). Remove from the oven and place on a cutting board. Let rest for 5 minutes. Slice steak into strips.