To prepare the sponge:
- Line a baking tray (30x40cm) with baking parchment paper or non-stick silicone mat.
- Preheat the oven to 200ºC.
- In a mixing bowl, combine the sugar and egg yolks.
- Split the vanilla pod and scrape the seeds into the bowl, or add the essence.
- With the paddle attachment, mix on medium speed until the mixture is pale and creamy.
- Add the flour in batches, mixing well after each addition.
- In a clean mixing bowl, whip the egg whites with the balloon whisk attachment on high speed until they stiff.
- Using a spatula, gently fold the stiff egg whites into the batter.
- Pour the cake batter onto the prepared tray, spreading out in a thin layer (1/2cm).
- Bake for about 10 minutes, or until cooked.
- Remove from the oven and transfer the sponge-along with the parchment paper - to another tray.
- Wrap with cling wrap while hot and keep in the refrigerator.
To prepare the butter cream:
- In a saucepan, combine the sugar and water, and cook until syrupy (121ºC).
- Place the egg yolks in a mixing bowl with the paddle attachment.
- Mixing on a low speed, pour the syrup in slowly; whisk until the mixture has cooled.
- Add butter and whisk on medium speed until creamy.
- Divide the cream into two equal parts.
- Stir the melted chocolate into one portion, and the coffee mixture into the other portion.
To roll the log:
- Peel the baking parchment paper from the sponge.
- Using a spatula, spread the coffee cream on the sponge and roll into a log.
- Trim the ends neatly.
- Cover the log with the chocolate cream.
- Drag the tines of a fork lightly through the surface of the cream to make it look like tree bark.
- Decorate to your liking.