Whirl ingredients in a food processor until smooth, about 2 minutes.
Lay a piece of plastic wrap on a work surface. Using a rubber spatula, scrape butter lengthwise onto plastic. Lift top edge of plastic up and over butter to meet bottom edge of plastic. Roll butter toward you, evening it out into a log about 4 in. long. Twist ends of plastic to seal. Chill until firm, about 30 minutes.
Remove plastic and slice off 1/4-in. portions (1 tbsp.) to serve over steaks.
Make ahead: Up to 1 week chilled, or up to 1 month frozen, wrapped in several layers of plastic.