Put the chocolate in a heatproof bowl and place over a saucepan of simmering water to melt, stirring occasionally. (Alternatively, melt gently in the microwave.)
When the chocolate has melted, add the creamed coconut and stir until blended. Gradually add the icing sugar and continue stirring, still above the saucepan of water, until the mixture is quite runny.
Beat the egg yolks into the chocolate, then take the bowl off the heat. Add the butter gradually, then allow the mixture to cool.
Add a pinch of salt to the egg whites and whisk until they stand in stiff peaks. Carefully fold into the chocolate mixture, then divide among four individual dishes and chill in the fridge for 6 hours or overnight until firm.
Decorate each mousse with a little grated, creamed coconut sprinkled on top and serve, if liked, with small dessert biscuits.
*For a more sophisticated flavour, sprinkle a few raisins steeped in dark rum in the bottom of the dishes. Or add 1 tbsp rum to the creamed coconut and melt it separately over a low heat, before blending it into the chocolate. *Use a good quality plain chocolate with at least 70% cocoa solids. *To melt chocolate in a microwave, break into squares, put into a bowl and microwave for 3–4 minutes on low power. Time will vary depending on the power of the microwave, so keep an eye on it as it melts.