1. Preheat the oven to 400°F. Heat a cast-iron pan over high heat. Season meat on both sides with salt and pepper to taste.
2. When the pan is very hot, add the oil and gently lay the steak in the pan. Brown the meat for 5 minutes. Turn the steak over, add the butter to the pan, and brown the meat for 5 minutes longer.
3. Turn the steak again. Then place the pan into the oven and cook for 10 minutes. Remove the steak from the pan and let it rest in a warm place for 10 minutes. Slice it into thin pieces, cutting on the diagonal.