Dan Lepard makes a stunning, yet simple icing with a strong chocolate flavour and dark colour.
Mix the cocoa and icing sugar in a bowl. Melt the butter for a few seconds in the microwave, or in a small pan over a low heat. Mix the melted butter and the cream into the sugar and cocoa, and stir until smooth.
Use while smooth enough to spread, or thin with a little boiling water for a runnier icing.