For the sponge cake
- Preheat oven to 180* C (350* F) Fan.
- Beat the egg whites in a mixer on low speed using the whisk attachment.
- Add the salt and 30 g of sugar. Turn up the speed and beat until you create a meringue with stiff peaks.
- In a clean mixer, beat the egg yolks along with 50 g of sugar with the whisk attachment for about 8-10 minutes, until the mixture becomes white and very fluffy.
- Melt the chocolate couverture in a bain marie.
- Allow it to cool to room temperature and add it to the yolk mixture. Mix with a spatula.
- Add ¼ of the meringue to add volume to the yolk mixture.
- Stir quickly with a spatula and then gradually add the remaining meringue and gently fold.
- Line a 30x40 cm baking pan with parchment paper and generously grease with butter and dust with cocoa powder so that the mixture doesn’t stick to it.
- Spread the mixture into the prepared baking pan and bake for 15-17 minutes.
- When ready, remove from oven, cover with a towel and allow it to cool for 2-3 hours until it softens.
For the chocolate ganache
- Place a saucepan over medium to low heat.
- Add the heavy cream and heat for 5-7 minutes, until it comes to a boil.
- Chop the chocolate into pieces and transfer to a bowl.
- As soon as the heavy cream comes to a boil, add it to the chocolate.
- Allow it to sit for a minute, until the chocolate heats up and then stir with a spatula until incorporated and you create a smooth ganache.
- Spread it in a 30x40 cm baking pan and stir with a spatula so that it can cool. It may take about 15-20 minutes.
For the log
- Spread a clean sheet of parchment paper on a working surface.
- Remove the parchment form the sponge cake and turn out onto the new sheet of parchment.
- Use a pastry brush to drizzle the cognac over the sponge cake.
- Spread 2/3 of the chocolate ganache with a spatula. Reserve some of the ganache to decorate the log at the end.
- Position the wide side of the sponge cake directly in front of you and start to roll it all the way to the end on the opposite side.
- Transfer to a wire rack and spread the remaining chocolate ganache over the log.
- Decorate with cherries and physalis fruit.
- Refrigerate for about 2 hours so it can chill and become firmer.
- When ready, dust with icing sugar and serve.