Preheat oven to 500 degrees F. Place cast iron skillet in oven . Coat steak lightly with oil.
Spread ground pepper on a plate. Press the steak onto the pepper, and then lift it up and put it down again several times, until the steak is covered with all the pepper it will hold. Turn steak and press pepper firmly into meat with the heel of your hand. Apply pepper the same way on the other side.
Heat burner on stove to high heat. Remove skillet from oven and transfer to stove. Place steak in middle of pan and cook for 30 second without moving. Turn and cook another 30 seconds, and then place skillet in the oven for two minutes. Flip steak and cook another 2 minutes (3 minutes per side for medium rare).
Remove steak from pan. Cover with foil and allow to rest for 2 minutes.
While steak is resting, pour cognac into pan. Stir into the juices in pan. Add butter and stir. Pour sauce over steak and serve.
Recipe from The Unofficial Mad Men Cookbook: Inside the Kitchens, Bars, and Restaurants of Mad Men by Judy Gelman and Peter Zheutlin (Smart Pop, 2011).