Pre-heat the oven to 180 degrees C. Line a swiss-roll or lamington tin with baking paper, cut and folded to give a depth of at least 4cm.
Cherries: Drain the cherries and discard the syrup, then place them in a shallow dish, spoon over the Kirsch and set aside.
Filling: Break the pieces of chocolate into a bowl and add 2 tablespoons of water. Melt the chocolate either in the microwave or in a bowl over simmering water then beat it with a wooden spoon until smooth
Next beat the 2 egg yolks until frothy. Add them to the warm chocolate mixture. As soon as the mixture has cooled, whisk the egg whites to the soft-peak stage then gently cut and fold them into the chocolate mixture. Cover the bowl with plastic wrap and refrigerate for an hour.
Cake: Whisk the 6 egg yolks until they begin to thicken. Add the caster sugar and continue to whisk, but be careful not to overdo this, stop when it falls off the whisk in ribbons. Fold in the sifted cocoa powder.
In a clean bowl, whisk the egg whites to the soft-peak stage. Fold one spoonful of the whites into the egg/cocoa powder mix and then gently fold in the rest of the egg whites.
Pour the mixture into the prepared tin and bake the cake on the middle shelf of the oven for about 20 minutes or until it's springy in the centre. It will look very puffy, but a little finger gently pressed into the centre should reveal that it is cooked. It's important not to overcook it; otherwise it will be difficult to roll.
Remove it from the oven (it will sink a little) until it's absolutely cold, and then turn it out onto another sheet of baking paper, which has been lightly dusted with sifted cocoa powder. Then carefully peel away the layer of paper that it was cooked on.
To Assemble: Strain the soaked cherries and pour the liquid it over the base.
Next remove the chocolate filling from the fridge and spread it carefully and evenly all over the surface of the base. Whip the cream softly and spread this all over the chocolate filling, leaving a good 2.5 cm border all round to allow for it spreading, then lightly press the cherries into the cream.
Rolling this cake up is going to be a lot easier than you think. All you do is take hold of the shorter edge of the baking paper, lift it and bring it over the top of the cake forcing it to roll up. Don't worry about cracks.
Topping: Serve on a platter, with drizzled chocolate, dusted cocoa powder or icing sugar.