Sprinkle your steak with salt and set a heavy (cast iron is ideal) skillet over medium-high heat.
Drizzle some oil into the skillet and when it’s hot, cook the steak for about 4 minutes, until a deep crust has developed on the bottom.
Flip the steak and add the butter to the pan.
Add the rosemary and shallot and as the butter melts, tip the pan and use it to baste the steak, cooking for another 4-5 minutes (for medium-rare), or until done to your liking.
Let the steak rest for 5-10 minutes before slicing and serving with the butter and shallot from the pan poured overtop.