Cut the pork fillet in two parts lengthwise and cut again each part in three, leaving the distal part attached to one side. Plait the meat and close the end with a toothpick. Cook the plaits on both sides in a large pan with olive oil and a bit of butter, season with salt and pepper and toward the end wet everything with a little of Traditional Balsamic Vinegar of Reggio Emilia and let it evaporate. When the meat is ready, lay it on a serving dish, meanwhile make the sauce reduce and when it is ready serve it aside the pork. If you like it, you can accompany this course with spinach cooked  with butter or a vegetable flan.