Make the garlic butter, in a small saucepan, melt the butter with rosemary, garlic, and pepper. When the butter starts bubbling, cook for 1 minute then remove from heat.
Check the temperature. For a medium rare steak, grill the steaks for about 4 minutes on each side until the internal temperature reaches 130°F/55°C.
When the steaks are done, remove from the grill onto a plate and pour the butter all over the steaks and cover with foil. Allow to rest for 5 minutes before slicing and serving.