Preheat oven to 180C/160C. Grease a 23cm x 32cm baking tray with sides. Line base and sides with baking paper.
Using an electric mixer, beat eggs and sugar for 6 to 8 minutes or until thick and creamy (mixture will form ribbons when falling from beaters). Fold in sifted flour and cocoa until just combined. Fold in chocolate. Pour mixture into prepared pan, spreading gently to level.
Bake for 12 to 15 minutes or until just firm to touch.
Meanwhile, dust a sheet of baking paper that’s slightly larger than the pan with extra sugar. Turn out cake immediately onto paper. Remove lining paper. Using paper as a guide, roll up from 1 short end. Wrap in a clean tea towel and set aside to cool completely.
Meanwhile, make Ganache: Place chocolate and cream in a microwave-safe bowl. Microwave on HIGH (100%) for 1 to 2 minutes, stirring with a metal spoon every 30 seconds, or until smooth and combined. Refrigerate for 30 minutes or until a thick spreadable consistency.
Unroll cake. Trim edges to neaten, if required. Leaving a 2cm border, spread cake with jam, then top with cream. Roll up cake to enclose filling. Discard paper. Place on a serving plate. Spread ganache all over cake. Refrigerate for 10 minutes or until just starting to set. Run a fork through the ganache to resemble wood. Refrigerate for 20 minutes or until ganache is set. Dust liberally with icing sugar. Serve