Chocolate Yule Log

Preheat the oven to 180°C fan (400°F/gas 6). 

Make the genoise: Separate the egg yolks and whites into two bowls. Add the sugar and warm water to the egg yolks and whisk energetically for a couple of minutes. Stir in the flour, cornflour, cocoa and the salt and mix together with a spatula. 

Finish the genoise: Add a pinch of salt to the egg whites and mix with an electric mixer for 5–7 minutes until stiff peaks form. Add half of the egg whites to the egg yolk mixture and whisk well. Fold in the rest of the egg whites gently, using a spatula. 

Lay some baking paper on a shallow baking sheet and spread the genoise evenly with a spatula. Cook for 10–12 minutes in the oven, until softly brown. 

Cover the warm genoise with a clean, damp tea (dish) towel. Turn the baking sheet upside down onto the towel, remove the baking paper, and roll up the genoise using the tea towel. Put in the fridge until completely cooled. 

Make the white chocolate mousse: Break the white chocolate into a medium heatproof bowl. Bring the cream to a boil in a pan over a medium heat, then pour over the white chocolate. Gently mix with a spatula until the white chocolate is fully melted. Transfer to the fridge until it is time to assemble the Büche. 

Next make the milk chocolate ganache. Roughly shred the chocolate with a knife into a large, heatproof bowl. Bring the cream to boil over a medium heat, then pour over the chocolate and let sit for 30 seconds. Use a spatula to gently whisk to create a silky smooth ganache, then whisk in the diced butter to melt. Place the bowl in the freezer to set for 30 minutes. 

Finally, make the syrup. In a pan, add the water, sugar and vanilla extract and bring to boil. Cook for 5 minutes until the syrup thickens. 

When you are ready to assemble the Büche, whisk the white chocolate ganache until light and soft using a handheld electric whisk, then fill a piping bag with the mix. Do the same with the milk chocolate ganache in a separate piping bag. 

Now it’s time to assemble the Büche. Gently remove the cloth inside the genoise and unroll the sponge onto a large piece of cling film (plastic wrap). Use a pastry brush to spread the syrup all over the genoise, then pipe the white chocolate mousse on top and roll it up again tightly using the cling film, securing it at each end. Put in the fridge for 15 minutes to set. 

When ready to serve, cover the rolled-up sponge with the milk chocolate ganache and create a wood effect by drawing lines in it with a spatula. Decorate with Christmas decorations and sprinkle with icing sugar.