Melt the chocolate in a small heatproof bowl set over a sauce pan of simmering water, stirring frequently. Let cool slightly.
In a mixer fitted with the paddle attachment, beat the butter on medium speed until light and creamy. Add the confectioners' sugar and vanilla and beat until blended. Add the chocolate and continue to beat until smooth, stopping the mixer once or twice to scrape down the sides of bowl.
To use as a buttercream frosting, spread onto cooled baked goods.
Recipe by Divine Party Concepts at http://divinepartyconcepts.com/2013/05/16/flavored-butters-recipe-and-book-giveaway/