Preheat the oven to 180°C.
Melt the dark chocolate with 30ml of water over simmering water and beat until smooth.
Beat two egg yolks into the warm chocolate and fold in whisked egg whites.
Chill the mousse mixture in the fridge for at least one hour.
Drain cherries and soak them in cherry brandy.
Whisk six egg yolks with caster sugar until ribbon stage, then fold in cocoa powder.
Fold whisked egg whites into the base mixture and pour into the prepared tin.
Bake in the middle of the oven for 20 minutes until springy.
Allow the cake to cool completely before turning out onto dusted greaseproof paper.
Drizzle the base with the cherry brandy and spread with the chilled chocolate mousse.
Top with whipped double cream and cherries, leaving a 2.5cm border.
Roll the cake using the paper and chill.
Melt additional chocolate on a plate, chill for 45 minutes, and create curls using a blade.
Glaze the roulade with warmed cherry jam and brandy, then decorate with curls and cocoa powder.