Chocolate icing

Mix 150 g icing sugar with 2 tablespoons cocoa powder, then stir in hot water a teaspoon at a time until it is thick but spreadable. Pour it over a completely cool traybake and leave it to set.

Let the sponge cool completely first. Icing on a warm cake can melt, run off the top and soak into the crumb instead of forming a neat layer.

Keep a cake with a simple icing-sugar-and-cocoa glaze in an airtight container in a cool, dry place. If the icing contains cream or another perishable ingredient, refrigerate the cake at 5°C or below.

A plain cocoa-and-icing-sugar glaze can turn sticky or patchy after thawing. For the best finish, freeze the uniced sponge, thaw it fully, then ice it; wrap it well to protect it from freezer smells.

It is a classic topping for chocolate sponge, chocolate fairy cakes and chocolate traybakes. A thin layer also works on plain sponge when you want a chocolate finish without adding a filling.

Yes. Spread melted chocolate over a completely cool cake for a firmer, snappier topping; unlike a cocoa-and-icing-sugar glaze, it will set quite hard, so cut the cake with a warm knife.

Chocolate icing is usually made with icing sugar and cocoa, often loosened with water, and sets into a sweet coating. Ganache is made by mixing chocolate with hot cream, so it is richer and stays softer.