Once I took a cake decorating class from Tom Lawson. His chocolate butter cream icing recipe is the BEST one that I have ever come across. It's creamy and delicious!
Special technique: Instead of creaming the butter and sugar first. Then, adding the remaining ingredients. It's the other way around.
In the bowl of an electric mixer fitted with a whisk attachment, add the sugar, Creme Bouquet, vanilla, salt, and hot water. Beat on high speed for 8 to 10 minutes. Turning off the mixer and scraping down the sides of the bowl occasionally.
At this point the icing will look like a thick pancake batter. If it is too thick add 1 T. hot water at a time until the desired consistency is made. Be careful not to add too much water. More can be added in the next step.
Add the butter, shortening, ganache and cocoa; continue whipping the icing until it is glossy and shiny.
The icing will keep refrigerated for a month. Bring to room temperature. Whip again.
This s enough icing for a 3 layer 8" cake.