Richard Bertinet’s Bûche de Noël (Yule log)

Method

1. For the sponge, preheat the oven to 180°C/fan160°C/gas 4, then grease and line 2 x 25cm x 38cm Swiss roll tins. Put the eggs, egg white, sugar and a pinch of salt in a mixing bowl and place over a pan of gently simmering water, whisking continuously for 6-7 minutes until light, voluminous and thickening.
2. Remove from the heat and continue beating at a high speed (in a food mixer or with a hand mixer if you wish) for 3-4 minutes until the mix is cool and leaves a trail on the surface when the beaters are lifted from it. In 3 batches, sift in the flour and cocoa powder by hand, folding in carefully with a metal spoon between each addition. Pour half the melted butter carefully into the mix and fold in. Repeat with the rest.
3. Divide the mixture carefully between the lined Swiss roll tins, tipping them so it gets into the corners. Bake for 15 minutes. Remove from the oven, cool in the tins for 2 minutes, then remove and leave to cool further on a wire rack.
4. For the syrup, put the sugar and 200ml cold water in a pan and bring to the boil. Boil for 10 minutes until all the sugar has dissolved. Stir in the kirsch and leave to cool.
5. For the chestnut and cocoa crème, split the vanilla pod lengthways and put it in a pan with the milk. Bring to the boil, then remove from the heat and discard the vanilla pod.
6. Mix the sugar and egg yolks in a bowl, then sift in the flour and cocoa powder. Pour over the hot milk and whisk. Return to a clean pan over a low-medium heat, then bring to a gentle simmer. Cook for 3-4 minutes, stirring all the time. It will form lumps, but keep whisking – it will become smooth and very thick.
7. Remove the cocoa crème from the heat and transfer to a cold glass bowl. Put the chestnut purée into a separate small bowl, mix in a little of the warm cocoa crème to loosen it, then fold the purée into the rest of the crème. Cover the surface with a piece of baking paper and leave to cool completely. Once cool, whisk the double cream until light and fluffy. Whisk the cold chestnut cocoa crème until loosened, then fold in the cream with a wooden spoon.
8. When you’re ready to assemble the log, turn out the sponges onto a sheet of baking paper with the rough tops face-up. Brush or dab the tops with some of the stock syrup, then spread the cocoa crème over with a palette knife, leaving a 2-3cm border at one of the short edges on each sponge.
9. Starting with the short end with the border nearest to you, roll up each sponge as tightly as you can. Get the first roll in using your fingertips to tuck it under, then lift the sheet of paper to support the sponge as you roll it forward. Once both sponges are rolled, dab or brush more stock syrup over the top.
10. Dust a work surface with icing sugar and roll out the marzipan to about 60cm x 25cm (it will be thin enough to be translucent). If you want to make one long log, you can now join the 2 small logs together – just lay them end-to-end. If you want to make 2 logs, cut the marzipan into 2 x 30cm x 25cm pieces. If you have a marble chopping board, transfer the log or logs to it, otherwise put it/them on a large chopping board.
11. Lay the marzipan over the log/s so it fits snugly. Mould it to the shape of the log/s and tuck it tightly under the sides and at the ends.
12. Roll little pieces of the extra marzipan into strips and use them to lay over the log/s at angles to look like whorls or rough bits of bark.
13. Melt the chocolate in a bowl set over a pan of simmering water (do not allow the water to touch the bowl). Little by little, pour the chocolate over the log/s. Do this gradually so it sets a bit at a time, letting you build up a rough, uneven, bark-like surface. (If the board fits, leave it in the fridge between each addition to speed up the process.) You may need to use a palette knife to encourage the chocolate to cover the log/s completely. Don’t worry that much of the chocolate runs out over the marble board – you’ll use it to make curls of bark. (If you’re not using marble, pour a little melted chocolate over a flat china or glass surface and leave to harden – use this to decorate the log/s later.)
14. Carefully lift the log/s onto a serving plate. Using a sharp knife and holding the tip of the knife in one hand and the handle in the other, angle the blade towards you. Drag it across the surface of the chocolate stuck to the marble (or poured over a smooth surface and hardened) to form shards and curls. Decorate the log with jasmine tea leaves (to look like moss), chocolate shards and curls and, if you wish, a little wine powder and gold leaf.