Place in the beef tenderloins, immediately turn the heat down to medium-high, add in the butter and cook for 2 to 2 ½ minutes on each side until very well browned.
Transfer the pan or pot to the oven and roast at 275° for 20 to 25 minutes or until it has reached a 120° to 125 internal temperature. Remove the beef from the pan and let rest for 3 to 4 minutes.