Grease and line a swiss roll tin.
Preheat oven to 180°C/350°F/Gas 4.
Beat the egg yolks with 125g caster sugar.
Add butter, plain flour, baking powder, 1 tbsp hot water and mix.
Beat the egg whites with a pinch of salt.
Gently fold the egg whites into the egg yolks.
Spread the batter onto the prepared baking tin.
Bake for about 12 minutes .
Remove from the oven and allow to cool.
To prepare the butercream icing, beat together the butter, icing sugar and melted chocolate.
Spread the sponge with the buttercream icing using a palette knife.
Roll up the sponge gently and carefully removing the baking paper.
Cut a small piece off the end of the log on the diagonal, this will become a branch.
Cover the outside of the log with the buttercream.
Place the extra branch on top of the log and cover with the icing.
Use a fork to create lines along the sides of the log.
Decorate the serving platter with the coconut.