Pre-heat the oven to 180C/350F/Gas 4.
Break the chocolate into a basin and add 2 tbsp of water. Place the basin over a saucepan of barely simmering water, making sure the basin isn't touching the water. Remove the pan from the heat and wait for the chocolate to melt before beating it with a wooden spoon until smooth.
Next beat the 2 egg yolks, first on their own and then into the warm chocolate mixture. As soon as the mixture has cooled, whisk the egg whites to the soft-peak stage then gently fold them into the chocolate mixture. Cover the bowl with clingfilm and leave it in the fridge for a minimum of an hour.
Drain the cherries, discard the syrup, then place them in a shallow dish, spoon over the cherry brandy and leave aside till needed.
To make the base: first place the egg yolks in a bowl and whisk them with an electric hand whisk until they begin to thicken. Then add the caster sugar and continue to whisk, but be careful not to overdo this, stop when it falls off the whisk in ribbons. Now fold in the sifted cocoa powder. Then, using a clean bowl and beaters, whisk the egg whites to the soft-peak stage. Then take 1 large spoonful, fold it into the chocolatey mixture to slacken it, and gently fold in the rest of the egg whites.
Now pour the mixture into the prepared tin and bake the cake on the middle 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 and leave it until it's absolutely cold, then turn it out on a sheet of greaseproof paper, which has been lightly dusted with sieved cocoa powder. Then carefully peel away the silicone paper.
Drain the cherries again in a sieve placed over a bowl to catch the brandy and sprinkle all but 1 tbsp of the liqueur all over the base. Next remove the chocolate filling from the fridge and spread it carefully over the surface of the base. Next whip the double cream softly, and spread this over the chocolate filling, leaving a 2.5cm/1in border all round, then press the cherries into the cream.
Take hold of one edge of the greaseproof paper beneath the cake, lift it and, as you lift, it will begin to come up. Just gently roll it over, pulling the paper away as it rolls.
Melt the chocolate as before, taking great care not to overheat it, then pour it on to an upturned plate 15cm/6in in diameter. Then place in the fridge for about 45 minutes until it's set. The chocolate should be firm when you touch it.
To make the curls use a cheese slicer, or a very sharp knife. Start at one end and just pull the slicer or knife along the surface of the chocolate towards you until curls form. Place them in a plastic container. Put the container in the fridge.
Now you can decorate the cake: spoon the jam into a small saucepan, add the reserved liqueur, warm gently and then brush over the surface. Place the chocolate curls all over. Finally dust the surface lightly with cocoa powder.