Rinse the meat, dry with a napkin, cut into portions about 2 cm thick, be sure to cross the fibers. The meat should only be at room temperature, not cold.
Pour the soy sauce mixed with olive oil over the meat and leave to marinate for 1-2 hours. You can marinate the meat in the evening, so it will be even more tender.
Preheat the pan. You do not need to pour the butter, as the meat is marinated in it. Optionally, you can add.
In a preheated skillet, fry the pork on each side for about half a minute.
Transfer the meat to the wire rack and send to the oven preheated to 150 degrees for 6-7 minutes under the grill. The meat will be medium rare with a light pink juice inside.
At the end of baking, remove the meat from the oven, salt to taste, let it rest for a couple of minutes so that the juice is evenly distributed over the piece.