• Preheat the oven to 180°C (Fan 160°C). Grease a 20cm deep cake tin and line with non-stick baking paper. If using a foil container, grease this well.
• Blend the cocoa with the hot water in a large bowl and leave to cool. Add the remaining cake ingredients to the bowl and beat with an electric mixer until light and fluffy.
• Spoon into the tin and bake in the preheated oven for 20 – 25 minutes, or until the cake has shrunk slightly from the sides of the tin and springs back when lightly pressed with a finger.
• Turn out, remove the paper and leave to cool on a wire rack. 
• To make the icing, measure the cocoa, butter, milk and icing sugar into a bowl. Beat well to a light, smooth consistency.
• Spread over the top of the cake and swirl attractively with a round-bladed knife. Leave to set before serving.

Recipe from Mary Berry’s Fast Bakes, Headline £26