Place the butter in the mixing bowl of a stand mixer or in a large bowl
Attach the flat beater, set the stand mixer to speed to 4 (medium speed), and beat for about 1 1/2 minutes or until creamy, scraping the sides as needed
Add the corn syrup and set to 6 (medium-high speed) for 1 minute
Set the mixer to stir and gradually add the powdered sugar, mixing until blended
Turn to speed 4 and beat for 1 minute
Turn to speed 2 (low speed) and gradually add the melted chocolate and mix for about 2 minutes
Increase speed to 4 for another minute, scraping the sides as needed