Preheat your grill or stovetop grill pan to high heat.
Rub both sides of the steak with sea salt and black pepper.
Place the steak on the preheated grill with olive oil and cook for 1-2 minutes on each side. Add the butter, whole garlic, and rosemary and cook both sides for 3-4 minutes for a medium-rare steak. Cook longer if you prefer it more done.
Let the steaks rest for 5 minutes, before slicing against the grain.
Notes
TO STORE. Store the leftover cooled steak in an airtight container in the refrigerator for 3 to 4 days.TO REHEAT. It’s best to reheat leftover steak in a baking dish in a 250ºF oven until the internal temperature reaches 110ºF. Heating it in a covered pan on the stove also works well.TO FREEZE. Freeze the leftover steak in a container or ziplock bag for 2 to 3 months.