Line a Swiss roll tin, 29cm x 18cm and about 2.5cm deep with greaseproof paper and oil very lightly.
For the roulade
Whisk the egg whites in a very clean and dry bowl until they reach the soft peak stage.
In a separate bowl, whisk the egg yolks and sugar until thick. Sift in the cocoa and gently stir in the whisked egg whites.
Pour into the lined tin and bake for 20 minutes. Remove from the oven and leave to cool in the tin, where it will sink dramatically.
Chocolate mousse
Put a little water into a saucepan and bring to the boil. Break the chocolate into a bowl and place over the water. Do not let the bowl touch the water. Add 2 tblsp milk, keep warming the chocolate until it melts and beat until smooth.
Now beat in the egg yolks.
Wait until the chocolate is cool and gently fold in the whisked egg whites.
When the roulade is cool, place a piece of greaseproof paper on the worktop and dust with icing sugar.
Now tip the roulade onto the sugared paper, and remove the lining paper on the bottom.
While the chocolate mousse is still soft, spread onto the cake and top with the cream.
Now firmly grasp the long edge of the greaseproof paper and tip the roulade over, starting a Swiss roll shape. Using the paper to help you, continue to roll the roulade, forming it with the paper when you need to. It will probably split, but that’s fine, it adds to its charm.
When you serve it, dust the whole thing with icing sugar.
Notes
This is a quality pudding, that really will serve 10. Lovely on its own, even better with a dollop of cream or ice cream.I generally use 2 x 100g bars and forget about the 25gLots of variations, you could use milk or white chocolate. Substitute flour for the cocoa in the sponge and you could vary it even more. Add a little vanilla and use your favourite jam instead of the mousse with the cream.Stay with the chocolate and add a little orange zest. Create a retro Black Forest by using black cherries or black cherry jam in the middle. Or have a look at the Victoria Sponge post for lots of other ideas