What you'll need
- Ribeye or Sirloin beef
- Oil, Butter, Salt, Pepper
What you'll do
Pat your steak dry, make sure it's not frozen or cold on the inside (20 mins outside the fridge should do), and season it with salt and pepper.
Heat your cast iron skillet on medium-low (if you cook the steak on high it turns all stringy). Put some oil and the rosemary in it and put your steak in the skillet. You should hear some nice fizzling. That's your steak searing.
After you've sear it on one side, turn it. After one minute, turn it, and so on.
After a few turns, put a knob of butter in the skillet. Now between turns, use a spoon to make sure some butter is covering the top side of your steak. Juicy!
How long should the steak cook for? I did mine for 12 minutes total for medium rare. Could be more, could be less. Only way to know for sure is experience with your combination of beef, skillet, and stove - or (if you want to cheat) a meat thermometer: rare 60°C, medium 70°C, well done 80°C.