Set out steak 10 minutes before cooking.

Heat a cast-iron skillet to medium-high heat (you want it very hot)

Add the butter to the hot skillet and swirl it around the bottom.

Gently place the steak into the center of the skillet and cook for 2 minutes on each side. (before you flip the steak, reduce the heat to medium)

While the steak is cooking, add the mushrooms and garlic to the skillet, tossing every so often to keep them from burning.

Tip the skillet to one side every so often and use a spoon to scoop up some of the butter to baste the steak.

Once done, sear the edges for 30 seconds on each side.

Let it rest on a plate for 10 minutes when it is done. Top with rosemary.