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.