Season the steak with salt and pepper to taste. Heat the olive oil in a skillet over medium-high heat. Cook the steak until nicely browned on the outside, and nearly cooked to your desired degree of doneness on the inside, 3 to 4 minutes per side for medium-rare. An instant-read thermometer inserted into the center should read 130 degrees F (54 degrees C). Remove the steak from the pan, and tent loosely with foil to keep warm.
Wipe the oil from the skillet, and pour in the red wine; simmer until reduced by half. Whisk the flour into the beef broth, then stir into the simmering red wine along with the rosemary and Dijon mustard. Return to a boil; cook, stirring constantly until the sauce reduces slightly and thickens. Keep warm over low heat.
Cut the meat from the bone, then slice into 1/3-inch thick pieces. Serve with the rosemary sauce.