Sprinkle your steaks with salt and set a large, 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 steaks and add the butter and mushrooms to the pan. Cook for another 4-5 minutes (for medium-rare), or until done to your liking.
Remove the steak from the pan, tent it with foil and let it rest for 5-10 minutes.
Continue cooking the mushrooms, sprinkling with salt, until they’re golden.
Remove from the pan, add another drizzle of oil and cook the broccolini, tossing with tongs until just tender and golden on the edges. (Alternatively, cook the steak and broccolini together on a preheated grill, and sauté the mushrooms in butter on the stovetop to serve on top.)