2.Preheat oven to 180°C (160°C fan-forced). Grease two 24cm x 32cm (9½-inch x 13-inch) swiss roll pans; line base with baking paper.
3.Break chocolate into small saucepan, add the water; stir over low heat until smooth.
4.Separate eggs. Beat egg yolks and sugar in small bowl with electric mixer about 5 minutes or until pale and thick. Beat in chocolate mixture until combined. Transfer to large bowl.
5.Beat egg whites in large bowl with electric mixer until soft peaks form. Fold about one-third of the egg white into chocolate mixture; fold in remaining egg white.
6.Pour mixture evenly into pans; level surface. Bake sponges about 20 minutes. Carefully turn sponges onto baking-paper-covered wire racks to cool; the sponges are thin and delicate, so remove the lining paper slowly to stop the sponge pulling apart and breaking.
7.Whip cream and essence in small bowl with electric mixer until soft peaks form.
8.Place sponges on board; trim edges to make two rectangles of the same size. Halve each sponge lengthways. Place one rectangle of sponge on a serving plate; spread with one-third of the cream mixture, top with another layer of sponge. Repeat layering, finishing with a sponge layer. Refrigerate 30 minutes.
9.To make dark chocolate ganache; bring cream to the boil in medium saucepan; remove from heat. Break chocolate into pan; stir until smooth. Stand about 15 minutes or until ganache is spreadable. Spread ganache over top of sponge. Refrigerate about 30 minutes before serving.
It is fine to use just 1 x 300ml carton (tub) of thickened cream. When spreading the cream mixture over the sponge, don’t go too close to the edges, the cream will spread a little when you add the next layers. To make dark chocolate ganache; bring cream to the boil in medium saucepan; remove from heat. Break chocolate into pan; stir until smooth. Stand about 15 minutes or until ganache is spreadable.