1.Preheat oven to moderate, 180°C. Lightly grease an 18 x 28cm slice pan. Line base and sides with baking paper, extending paper 2cm above edge of pan.
2.In a large bowl, combine butter, sugar and egg. Stir in combined sifted flours and cocoa. Fold coconut through. Spread into prepared pan, smoothing top.
3.Bake for 15-20 minutes, until firm. Cool completely in pan.
4.To make icing, combine coffee and water, stirring until coffee dissolves. Add icing sugar and butter, and mix well. Stir in enough hot water until icing is a spreadable consistency. Spread over slice.
5.Cut into squares. Serve dusted with cocoa and grated chocolate.