Remove the beef from its packaging and let it rest on the counter at room temperature for one hour before cooking.
Heat oven to 275 degrees.
Using your hands, rub the tenderloin all over with the olive oil, sprinkle liberally with the salt and pepper, and place it on a sheet pan.
Place the sheet pan in the oven and roast for 1 hour. Check the temperature at the center of the roast. You are shooting for 125 degrees for rare, up to 135 for medium rare. When it comes to temp, let it rest under tented foil for 10 minutes, then slice and serve on a platter with melted rosemary butter alongside.