Heat a large, well-seasoned cast iron skillet over high heat. Pat the steaks dry with a paper towel, season with salt, to taste, and coat the meat the black pepper. Put the steaks in the hot skillet and cook until blackened and the steaks have released themselves from the pan. Turn the steaks and transfer the pan to the oven. Roast until an instant-read thermometer registers 125 degrees F for medium-rare, or cook until desired doneness.
Remove the pan from the oven and transfer the steaks to a cutting board; cover with aluminum foil to keep warm. Put the skillet back over medium heat. Carefully add the brandy and ignite it with a long kitchen match, to burn off the alcohol. Add the cream, and vinegar, and simmer until very thick. Stir in the butter just before serving.