Step 1

Remove your steak or steaks from the refrigerator and allow it to warm up slightly to room temperature for about an hour. Starting with a steak that is closer to room temperature helps with the even doneness we’re striving for.  While the steak is warming up, cut just a sliver of the fat from around the edge of the steak and place it back in the refrigerator. We’ll use that later.

Step 2

Season liberally with kosher salt and pepper, or your favorite steak rub. Insert a reliable leave-in thermometer into thickest portion of the steak.

Step 3

Place the cast iron pan in the oven and preheat the oven to 225° F.

Step 4

Place steak on a cooling rack, and place rack in a baking sheet. I cover the baking sheet with foil just to cut down on the cleanup later.

Step 5

Place steak in oven until it reaches an internal temperature of 125° F; about 45 minutes depending on the size of the steak. (This is the timing for medium rare; cook to your desired temperature.)

Step 6

Remove steak from oven and let rest while continually monitoring the internal temperature on the leave-in thermometer. Temperature should peak at around 129–130°F (usually about 7–8 minutes).

Step 7

While steak is resting, place the preheated cast iron pan over medium-high heat on stovetop. Then, place that sliver of fat we removed earlier into pan and allow it to render down. This is what we are going to sear the steak in. Once the steak's internal temperature has peaked and starts decreasing, add a sprig of rosemary to the rendered beef fat, and crank the heat under the cast iron pan to max for about a minute.

Step 8

Place the cooked steak directly onto the scorching hot skillet, flipping every 30 seconds for about 5 minutes total to develop that dark crust.

Step 9

Remove steak from the cast iron pan and top with compound butter. Slice and serve immediately.