I don’t have a specific recipe for chocolate icing, it’s just whatever amount of icing sugar I think will cover the cake, enough cocoa to give it colour and taste and either 1/8 teaspoon of instant coffee or vanilla to take a bit of the bitterness away from the cocoa that was added. Very hot tap water or boiling water to make to the consistency that I’m after for that cake, a little water goes a long way.
If you wish to make your chocolate icing that bit richer try adding a table spoon of drinking chocolate before adding water. Make sure you mix well.
I always sift my icing sugar and cocoa so would add the drinking chocolate to this.
I use what’s called icing mixture it has a little cornflour added to the mix to stop it hardening, I don’t use what’s called pure icing sugar.
Give it whirl next time you ice your chocolate cake and see what you think.