Preheat oven 170 degrees centigrade or 325 degrees farenheight
Combine the butter and sugar together in a stand mixer or by hand and mix until smooth and creamy
Sift the flour cocoa and baking soda into the butter and sugar mixture
Combine gently until completeely combind
Grease a flat baking sheet with some butter
Using a tespoon scoop a large blob of the mixture and roll it up in your hands then place on the baking sheet and press lightly to flatten down (make around 12 small cookies or 8 larger ones)
Cook for 10-12 minutes - the cookies will still be soft until cooled
Remove from the oven and set aside for 15 minutes to cool
In the meantime combine the ingredients for the iced topping
When the cookies are completely cooled spoon over the topping
As an optional extra cover with some sprinkles, food glitter, or fresh fruit for some extra color
