1/2 cup butter, softened
3 1/4 cups pwd sugar
1/4 cup unsweetened cocoa pwd
1/4 cup whipping cream, or more (I've found I always need more to get a spreading consistency. Of course, you can use milk, but it tastes better with the cream.)
1 (1-oz) square unsweetened chocolate, melted
2 tbsp light corn syrup
Place butter in a bowl and beat until creamy. Gradually add the pwd sugar, cocoa and salt alternately with the whipping cream and 1-oz melted unsweetened chocolate, scraping bowl often and beating well after each addition. stir in the corn syrup and beat until smooth and satiny.