Trim silvery skin from pork. Combine brown sugar and cajun seasoning, then rub the mixture into the meat.
Preheat oven to 425 degrees.
Heat butter or olive oil in a large, oven safe skillet. Sear tenderloin for two minutes per side to brown, then slide the skillet into the oven.
Roast for 18 minutes, then remove from the oven and tent with foil. Allow to rest for 5-10 minutes before slicing into 1/2 inch thick medallions.
Pork tenderloins can weigh anywhere from 1-2 pounds each. The recipe calls for 2 1/2 pounds, which is typically two tenderloins. To ensure even cooking, be sure to use two tenderloins that are similar in size and weight.