Preheat the oven to 180˚C/350˚F and line a 25 x 35 cm (10 by 14 inch) baking tray with baking paper.

To make the cake, first separate the eggs. Whisk the egg whites with a pinch of sea salt until stiff. Gradually beat in the icing sugar, then the egg yolks one at a time until very pale and light. Sift in the self-raising flour and cocoa powder, add the vanilla and fold in with an iron spoon to keep as much air in the mixture as possible.

Pour the dough into the prepared baking tin, smoothing it down gently and evenly. Bake for about 8-10 minutes or until the cake is cooked and springs back when pressed.

With the long side facing you, fold the cake with the paper in between. This will prevent the cake from sticking together as it cools. Allow to cool completely.

For the filling, whip the cream with the icing sugar until soft peaks form.

Roll out the cake on a floured surface and remove the baking parchment.

Spread the cake with the Nutella. Spread to the edges and repeat with the cream.

Grate the mandarin on top. Roll up the chocolate roll again (this time without the paper in between) and return to the fridge.

Meanwhile, make the butter cream. Melt the chocolate in a water bath, remove from the heat and leave to cool.

Cream the butter in a food processor until pale, then slowly add the icing sugar and melted chocolate. Allow to cool slightly so that it is not too thin. You can leave it in the fridge for a while if you like.

Take your log out of the fridge and cut off about a quarter at one corner. This will be your branch. Place it on your cake platter or board as shown and use some buttercream to hold the branch in place.