A classic Yule log that's a simple but gorgeous combination of light sponge and chocolate mousse. Have fun decorating with meringue mushrooms, grated chocolate, holly leaves and more, or simply leave plain and tuck in!
Preheat oven to 180 C / Gas 4. Line a Swiss roll tin with parchment.
Beat together the egg yolks and sugar till pale and creamy. Add the flour and mix till smooth. With a clean whisk, beat the whites to stiff peaks with the salt. Fold the egg whites into the yolk mixture, working gently to preserve as much air in the mixture as possible. Tip into prepared tin and smooth the surface.
Bake for 10 to 15 minutes in the preheated oven. Remove from oven and immediately turn out the cake onto a damp tea towel. Peel off the parchment and discard. Using the towel, roll the sponge up from one of the short ends, and leave to cool while you prepare the mousse.
For the mousse:
Set a heat-proof bowl over a pan of barely simmering water, ensuring that the bowl does not touch the water. Add the chocolate and leave to melt, stirring till smooth. Once melted, add the egg yolks and mix well. Remove from heat.
With a clean whisk, beat the whites to stiff peaks with the salt. Gently fold whites into the melted chocolate.
Unroll the cooled sponge carefully. Spread half of the chocolate mousse over the sponge, then snugly roll it up again. Wrap in cling film and place in the fridge for 1 to 3 hours (also cover the remaining chocolate mousse and place in the fridge).
After chilling, remove the cling film and place the log on a serving plate. Spread remaining chocolate mousse over the entire surface. With a fork, create a 'bark' effect by dragging the tines across the mousse. Chill till serving (best if chilled for 3 hours in advance of serving).