1 Remove steak from refrigerator 2 hours before cooking to bring to room temperature (only do this with whole cuts of meat, never with ground meat.) Rub dry mustard into both sides of the steak. Add salt and freshly ground pepper. Use a meat pounder to even out the thickness of the steak if necessary. Cut away any tough connective tissue on the surface of the steak.
2 Heat a large, cast iron skillet to medium high heat. Rub soft butter over both sides of the steak and place in pan. Let cook for 2-3 minutes on each side, check before flipping to make sure it has nicely browned.
At this point, if you have a steak only an inch thick or less, you can take the skillet off the heat and just let the steak sit for several minutes in the skillet, which will retain enough heat to cook the steak to medium rare. You can test for doneness by using a small sharp knife and cutting into the center to check the color. Also, if the steak is brown on both sides and it is weeping red juice, it's done.
3 If you have a thicker steak, you can finish it off in the oven, at 325Â°F for 15 minutes or so. Use a meat thermometer to test the internal temperature of the steak. It will be done at 130Â°F for medium rare. If you are using the oven method, when done, remove from the oven and let sit for 5 minutes.
You want to cook the steak only to medium rare, as cooking it further will make it more tough.
4 Slice the steak thinly, against the grain, on a diagonal.