Season the steaks on both sides with the rub. Heat the oil in a large skillet over medium-high heat. Sear each steak for about 3 minutes on each side for medium-rare, 4 minutes for medium. Transfer to a warm platter.
Add the flour to the skillet, and reduce the heat to medium. Stirring constantly for about 3 to 4 minutes, make a dark brown roux, the color of chocolate.
Add the onions, bell peppers, celery, salt, cayenne, and black pepper. Cook, stirring constantly, for 4 to 5 minutes, or until the vegetables are wilted. Add the stock and raise the heat to medium-high. Bring to a boil, add the steaks, and continue stirring the sauce until the mixture thickens, about 6 minutes. Turn the steaks several times during this coking time, basting them with the sauce. Add the mustard, blend, and simmer for about 2 minutes.
Yield: 2 servings