Melt the chocolate with the measurement water in a heatproof bowl set over a saucepan of gently simmering water (don't let the base of the bowl touch the water). Beat together the remaining cake ingredients in a large bowl until smooth and creamy. Stir in the melted chocolate.
Divide the mixture evenly between 2 greased and base-lined 20 cm (8 inch) sandwich tins (see
Make the frosting. Put the cream and creamed coconut into a small saucepan and heat gently until the coconut has melted. Turn into a bowl, then beat in the icing sugar and lime juice until smooth. Use half the frosting to sandwich the cakes together. Spread the remaining frosting over the top. Decorate with coconut shavings or shreds, if liked.