Preheat the oven to 180C/350F/160FAN/Gas4.
Line the baking tray with baking parchment.
Break up the chocolate and place in a saucepan with the coffee granules and water. Stir over a medium heat while the mixture melts and is well combined. Leave to cool while the remaining ingredients are prepared.
Separate the eggs then whisk the egg yolks in a bowl for about 5 minutes with all the sugar, less one tablespoon, until the whisk leaves a trail of mixture behind.
Fold the egg yolk mixture into the chocolate with a large metal spoon.
Whisk the egg whites to stiff peaks then whisk in the remaining tablespoon of sugar. Fold one tablespoon of the egg whites into the chocolate mixture with a metal spoon then tip the rest of the egg whites in and carefully fold until just combined.
Pour the mixture into the lined tin.
Bake for 15 to 20 minutes until set.
Leave the cake in the tin to cool and cover with a clean tea towel.
Put the cream in a bowl and whisk to medium peaks until it holds its shape.
Lay a clean sheet of baking parchment onto the work surface and sprinkle a tablespoon of the icing sugar.
Turn out the sponge on the clean parchment and carefully peel off the used parchment then trim any uneven edges with a bread knife.
Spread the cream in an even layer avoiding the edges and sprinkle over chopped cherries.
Turn the sponge until the shorter edge is in front of you. Make a slit with a knife, halfway through the sponge, about 2cm or an inch along the short edge. Use the parchment to help roll up as tightly as possible then place on a plate with the seam underneath.
Dust with icing sugar to serve.