Unwrap and place steak on cutting board, allowing it to warm up at room temperature for about an hour. Remove just a sliver of the fat from around the edge and place back in refrigerator.
Season liberally with Butcher Shop Steak Rub and insert meat thermometer.
Preheat your oven to 225-235 degrees.
Lay steak on a cooling rack, and place the rack on a baking sheet.
Place steak in oven until it reaches an internal temperature of 125-degrees before searing, this should take about 45 minutes depending on the size of the steak.
In hot cast iron pan, add the sliver of fat removed earlier and allow it to render down. Add a sprig of rosemary to the rendered fat.
Place steak directly onto the scorching hot cast iron, flipping every 45 seconds. Do this for about 5 minutes or until desired level of dark crust develops.