Preheat the oven to 500°F. Let the steak come to room temperature, then season generously with your favorite seasonings.
Heat a cast iron skillet over medium-high heat. Melt 3 tbsp of butter until sizzling.
Sear the steak for 3-5 minutes on each side, depending on thickness.
Transfer the skillet to the oven. Add a little extra butter and fresh rosemary sprigs on top of the steak.
Cook for 5 minutes or until the steak reaches your desired doneness (medium-rare: 130-135°F). Use a meat thermometer for accuracy.
Rest the steak for 5 minutes before serving. Enjoy!