Melt the Galaxy chocolate in the microwave in 30-second blasts until smooth. Set aside to cool.
In a large bowl beat the butter until really soft and pale in colour.
Sift in the icing sugar and cocoa powder into the bowl, and beat together until creamy and smooth.
Now pour in the melted Galaxy chocolate and fold together until combined.
Pipe on top of cupcakes or use to fill and cover a cake.