Heat a cast-iron skillet over medium-high heat. Rub pepper evenly over the steaks. Sprinkle salt over bottom of pan. Add steaks to pan; cook 2 minutes on each side or until browned. Remove steaks from pan; set aside.
Stir in port and broth, scraping pan to loosen browned bits. Reduce heat to medium. Return steaks to pan; cook 2 minutes on each side or until desired degree of doneness. Remove steaks from pan. Reduce liquid to 1/4 cup. Remove pan from heat. Add butter to pan; stir with a whisk until melted. Drizzle sauce over steaks.