Season the steak with salt, pepper and rosemary on all sides and return to the fridge for an hour or two if you have the time (not necessary).
Preheat the grill with burners in the up position for 10 minutes with left burner set to high, middle burner to medium and right burner off.
Lower the burners to the bottom postion and set the left and middle burners on low and place the steak over the left burner searing for 5 minutes per side.
Move the steak to the right burner location and close the lid baking for up to 30 minutes, check the intenal temperature with an accurate digital instant read thermometer.
Remove the steak when it hits your target internal temperature (make sure the thermometer tip is as close to the center of the steak as possible - indicated by the temperature settling at the lowest reading).
Let the steak rest for 5-10 minutes before slicing with your favorite sharp knife.