Position oven shelves; preheat oven to 180 C. Grease 25 cm/30 cm swiss roll pan; line base with baking paper. Combine chocolate, water and coffee in large heat proof bowl; sit bowl over saucepan of simmering water. Using wooden spoon, stir until chocolate melts then immediately remove bowl from fire.
Beat egg yolks & sugar in small bowl with electric mixer until thick & creamy; this will take about 5 minutes. Using large metal spoon, fold egg mixture into warm chocolate mixture. 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 preheated oven about 10 mins.
Meanwhile, place a 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 a tea towel. Cool cake to room temp.
Beat cream & kirsch in small bowl with electric mixer until firm peaks form. 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. Dust with cocoa powder. Cover roll; refrigerate 30 minutes before serving. You can also dress up the roulade with cherries or by piping some cream on top.
Drain cherries, reserving 1/4 cup (60ml) of syrup. Using knife, chop cherries coarsely. Using wooden spoon blend cornflour and reserved syrup in a saucepan. Add cherries; stir over heat until mixture boils and thickens. Remove from heat, cool to room temp.