Fork both sides of the steaks. Mix together the herbs from Provence and the mustard in a bowl and rub over the steaks.
Heat a large cast iron skillet to medium high. Add 2 tablespoons of the butter, and when melted, add steaks. Let brown on one side for 6 minutes. Turn over and brown the other side for 4 minutes for a medium-rare steak.
Transfer to cutting board, season with pepper and top with the remaining butter. Thinly slice steak and serve.