Prepare a shallow baking tin measuring 33cm x 23cm by greasing it and then lining with greaseproof paper

Make the cake by firstly melting the dark chocolate, either in a bowl over a saucepan of boiling water or in the microwave, checking and stirring every 30 seconds

Whisk the egg whites in a large bowl until stiff and forming 'peaks'

Place the egg yolks in a separate bowl with the sugar and whisk for around 3 minutes until pale and creamy

Pour the cooled melted chocolate and cocoa powder into the egg yolk and sugar mix and gently stir together until combined

Finally fold a couple of spoonfuls of egg white into the mixture until all the egg white is combined into the mixture. Don't over mix of you'll loose the air you need to create a light sponge

Pour the cake mixture into the prepared tin and bake in a pre-heated oven at 180 degrees/160 degree fan/gas mark 4 for 20 - 25 minutes until risen and firm to touch

While the cake is baking make the filling

Melt the chocolate as before

Place the chestnuts, milk, icing sugar and melted chocolate into a small food processor or blender and combine until smooth

Set aside until the cake is cold

Make the ganache by gently heating the coconut milk. Once steaming, add the dark chocolate and stir until you have a thick sauce

Place your filled sponge on a serving board or plate. If you want to make it look like a log cut a small piece off the end diagonally then join that to the side of the roll. It doesn't need to be neat because you will hide the join with your chocolate ganache

Cover the roulade with your chocolate ganache. I piped mine to get the effect of bark, but you can just spread it on if you prefer

Decorate any way you like and add a sprinkling of icing sugar for the finishing touch