I've been using this recipe for ages and I can't really say were it came from but I do know that no baker should be without a frosting like this. It's deceptively simple to prepare; the only important part is to bring the sugar and heavy cream to a rising boil. It's thick and fudgey and hard to resist eating right out of the bowl. Let is chill and then come back to room temperature and it goes on like buttah! —almacucina
Finely chop chocolate and transfer into the bowl of a stand mixer. Cut butter into small pieces and add to bowl. Mix on low just to combine.
Pour heavy cream into a medium size heavy bottomed pot; whisk in sugar. Heat on medium-high, whisking occasionally, until mixture comes to a rising boil. Remove from heat and add to chocolate mixture; let sit for one minute.
Mix on low, scraping down the bowl as necessary, for 1 or 2 minutes. Refrigerate for 1 hour and bring to room temperature before using.