Step 1

Melt the butter and the chopped chocolate together in a small bowl over a double boiler. When completely melted and uniform, set aside to cool to room temperature.

Step 2

In the bowl of an electric mixer fitted with the paddle attachment, beat together (starting on low) the cocoa powder, vanilla, half the icing sugar, the cooled melted chocolate mixture, and the sour cream. When the mixture is smooth, add the rest of the icing sugar, and continue beating til it’s smooth and fluffy.