For the filling, take a clean bowl and add the other half 0f teh butter and sugar; cream them together until pale and fluffy. Add the beaten egg gradually whilst mixing. (If it looks like it is curdling before you have added all the egg add a tsp of flour this should stop it curdling any further.) Now take the coconut,cocoa powder and flour and mix them together. Using a desertspoon, add a spoonful at a time and fold the coconut, cocoa and flour into the mixture, if needed add a small amount a cold water to give a soft dropping consistency.