4oz soft blue cheese, torn into small pieces or crumbled
Chopped fresh parsley
Allow the tenderloin to sit out at room temperature for 1 hour before cooking.
Preheat oven to 400℉.
Sprinkle tenderloin all over with 1½ teaspoons salt and 1 teaspoon pepper. If the tenderloin is tapered (thinner at one end), fold the tapered end back and use kitchen twine to secure it to the tenderloin. This will prevent the thinner part from overcooking.
In a heavy skillet, such as cast-iron, heat 2 tablespoons oil until very hot over medium-high heat. Place the tenderloin in the pan and brown the roast, turning occasionally, on all but one side, 3-4 minutes per side. If the roast is browning very quickly, turn down the heat to medium.
Turn the tenderloin so the unseared side is facing down, then place the skillet in the oven. Roast until cooked to the desired doneness, 15-25 minutes, the lesser amount of time for a smaller roast and the greater amount of time for a larger roast. For medium-rare the internal temperature should be about 120℉, and for medium it should be about 130℉.