3 Sift the flour with the cocoa. Fold the cornflakes into the butter mixture, then shape into rounds on a baking sheet. Bake for 20 minutes then let cool.
4 Sift the icing sugar with the cocoa. Add the butter and vanilla then stir in enough boiling water to make a smooth icing and ice the biscuits.
Chef's tip
The quality of the cocoa can make a huge difference to the outcome of both the flavour of the biscuits and texture of the icing on the afghans. Take the time to find a pure cocoa product without additives. A small jar of the best quality cocoa you can afford may be pricey, but it's worth it to get such a delicious result.