1.Position oven shelves; preheat oven to 180°C. Grease 25cm x 30cm swiss roll pan; line base with baking paper.
2.Combine chocolate, water and coffee in large heatproof bowl; sit bowl over saucepan of simmering water. Using wooden spoon, stir until chocolate melts then immediately remove bowl from pan to bench.
3.Beat egg yolks and sugar in small bowl with electric mixer until thick and creamy; this will take about 5 minutes. Using large metal spoon, fold egg mixture into warm chocolate mixture.
4.Beat egg whites in small bowl with electric mixer until soft peaks form. Using metal spoon, gently fold egg whites into chocolate mixture, in two batches. Spread mixture into prepared pan. Bake in moderate oven about 10 minutes.
5.Place large sheet of baking paper on board; sprinkle with extra sugar. Turn cake onto sugared baking paper; carefully remove lining paper, cover cake loosely with tea-towel. Cool cake to room temperature.
6.Beat cream and kirsch in small bowl with rotary or electric mixer until firm peaks form.
7.Meanwhile, to make cherry filling, drain cherries, reserving ¼ cup (60ml) of syrup. Using knife, chop cherries coarsely. Using wooden spoon, blend cornflour and reserved syrup in small saucepan. Add cherries; stir over heat until mixture boils and thickens. Remove from heat, stir in kirsch; cover surface of mixture with plastic wrap, cool to room temperature.
8.Spread cake evenly with cooled cherry filling then spread kirsch cream over cherry mixture. Roll cake from a long side, using paper to lift and guide the roll; place on serving plate. Cover roll; refrigerate 30 minutes before serving.
This cake must be made on the day of serving. To successfully make this cake, it is vital that the egg yolk/sugar mixture is beaten until thick and that the egg whites are beaten only until soft peaks form. Overbeating will dry out the egg whites and make it difficult to fold them into the chocolate mixture. Unrolled and unfilled cake can be stored, covered with a piece of baking paper then a damp tea-towel, overnight in the refrigerator