Preheat oven to 425 degrees. Line a roasting pan with foil, then place a roasting rack over top.
Carefully trim excess fat from the tenderloin, if necessary. Season with salt, pepper and paprika. Place on the rack and bake for 30 minutes.
Remove the tenderloin from the oven and brush the sides and top with the dijon mustard, then gently press the brown sugar into the mustard. Reduce oven heat to 375 degrees.
Return to the oven and bake for 15-20 minutes (maybe more depending on the size of the tenderloin) or until it reaches an internal temperature of 155 degrees. Remove from the oven and baste with the drippings. Cover with foil and allow to rest for 10 minutes before cutting and serving.
Notes
-For a little kick, try adding a pinch or two of cayenne pepper!