3. Preheat oven to 350 degrees F. Butterfly the tenderloin and pound it to an even thickness using a meat mallet or heavy skillet. Season both sides generously with salt and pepper.
4. Place the stuffing towards the bottom of the meat, lengthwise, and roll it up jelly-roll style. You may have more stuffing than you need. Secure shut using kitchen twine or toothpicks.
5. Heat remaining Tbsp butter in a large oven-proof skillet over Medium-High heat. Sear tenderloin on top and bottom sides for 4 minutes per side; sear remaining sides for 1 minute per side. (Be sure to use a splatter screen for this.)
6. Place skillet in the oven and roast tenderloin for 20-30 minutes, until tenderloin reaches desired degree of doneness.
7. Remove from oven and allow meat to reabsorb its juices for 10 minutes before slicing.