Chocolate ganache for the Yule log

1. Chop the dark chocolate and place it in a heatproof bowl.
2. Melt it over a bain-marie or in the microwave in 20–30 second bursts, stirring between each.
3. Heat the cream in a small saucepan until it just begins to simmer (do not boil).
4. Pour the hot cream over the chocolate in 3 additions, mixing well after each one.
5. At first the mixture may look grainy, then it will become smooth and glossy.
6. Add the butter in pieces and stir until completely melted and incorporated.
7. Let the ganache cool to room temperature, then place it in the fridge.
8. Stir from time to time so it thickens evenly.
9. It is ready when it has the texture of a chocolate spread: not too runny, not too firm, easy to spread on the sponge.

Preparing the cocoa Swiss roll sponge (light génoise)

1. Line a rectangular tin of about 25 x 40 cm with baking paper.
2. Lightly butter the paper to make unmoulding easier.
3. Preheat the oven to 180°C / 350°F, preferably on fan setting.
4. In a bowl, mix the flour, cocoa and baking powder.
5. Sift everything to remove lumps and obtain a fine powder.
6. This step helps the dry ingredients fold easily into the egg foam without deflating it.
7. In a large mixing bowl, add the eggs, sugar and vanilla sugar.
8. Whisk with a stand mixer or electric whisk for 8–10 minutes: the mixture should triple in volume, become very pale, dense and airy. When you lift the whisk, the ribbon that falls should sit on the surface for a few seconds.
9. Add the tablespoon of white vinegar to the egg foam and whisk a few seconds to combine.
10. The vinegar makes the sponge softer and easier to roll.
11. Add the flour/cocoa/baking powder mixture one spoonful at a time.
12. Fold in gently with a spatula, lifting the batter from the bottom to the top without whisking.
13. The goal is to keep as much air as possible in the batter for a light sponge.
14. Pour the batter carefully into the prepared tin.
15. Smooth the surface with a spatula so the layer is even.
16. Bake for 10–12 minutes: the sponge should be lightly golden, soft to the touch and spring back when pressed.
17. As soon as it comes out of the oven, prepare a clean, slightly damp tea towel.
18. Turn the hot sponge out onto the towel.
19. Gently peel off the baking paper.
20. Immediately roll the sponge up with the towel, without pressing too tightly, and leave to cool completely like this.
21. This step “trains” the sponge into a rolled shape and helps prevent cracks when assembling.

Assembling the chocolate ganache Yule log

1. Take the ganache out of the fridge a little before assembling so it becomes easy to spread.
2. Carefully unroll the cooled sponge.
3. Trim the edges slightly if needed for a neater roll.
4. Spread a generous layer of chocolate ganache over the whole surface, leaving about 1 cm free along one short edge to stop it overflowing when rolled.
5. Roll the sponge up again tightly, using the tea towel to help.
6. Wrap the roll in aluminium foil or cling film.
7. Place in the fridge for about 30 minutes so the log firms up and holds its shape.
8. Remove the foil.
9. Cut one end of the log at an angle.
10. Attach this small piece to the side of the log with a little ganache to imitate a side branch, like a real log of wood.
11. Cover the main log and the small “branch” with the remaining chocolate ganache.
12. Roughly smooth the surface, then use a fork to draw lines all over to mimic tree bark.