Delia's Squidgy choc log

This one's from Delia! Thanks Delia!

http://www.deliaonline.com/recipes/type-of-dish/party-food/roulade/squidgy-chocolate-log.html

Ingredients
 6 large eggs, separated
 5 oz (150 g) caster sugar
 2 oz (50 g) cocoa powder
For the filling:
 8 oz (225 g) dark chocolate (70-75% cocoa solids), broken into small pieces
 2 large eggs, separated
 8 fl oz (225 ml) double cream
To finish:
 icing sugar
 Pre-heat the oven to gas mark 4, 350°F (180°C).

Equipment
You will also need a tin 30 x 20 x 2.5cm / 12 x 8 x 1 inch, oiled and the base lined with baking parchment


Begin by making the chocolate filling. Break the chocolate in pieces into a basin and add 100ml/4fl oz warm water. Now place the basin over a saucepan of barely simmering water and wait for the chocolate to melt. After that, remove from the heat and beat it with a wooden spoon until smooth. Next beat the egg yolks, first on their own, then into the warm chocolate mixture. Let it cool a bit then whisk the egg whites till stiff and fold them into the chocolate mixture. Cover the bowl and chill in the refrigerator for about an hour.
Meanwhile you can get on with the cake. First place the egg yolks in a basin and whisk until they start to thicken, then add the caster sugar and continue to whisk until the mixture thickens slightly – but be careful not to get it too thick. Now sift the cocoa powder into the egg yolk mixture and whisk them together, then, using a clean whisk and bowl, whisk the egg whites to the soft peak stage. Next carefully cut and fold the egg whites into the chocolate mixture – gently and thoroughly – then pour the mixture into the prepared tin.
Bake the cake on the centre shelf for 20-25 minutes until springy and puffy. When the cake is cooked, remove it from the oven but leave it in the cake tin to cool (it will shrink quite a bit as it cools but don't worry, that's normal).
Then when the cake is quite cold, turn it out on to an oblong of baking parchment which has been liberally dusted with icing sugar. Peel away the cake tin lining paper from the bottom of the cake (which is now facing upwards), then spread the chocolate mousse filling over the cake. Next whip the cream softly and spread it over the chocolate filling. Now with the shortest end nearest you, roll the cake away from you, using the parchment to help you to make a log shape. This will serve eight people and, although it's unlikely that there will be any left, you can cover any remaining cake with an upturned basin and keep it in the refrigerator. As an alternative, an 11 oz tin of sweetened chestnut purée (crème de marrons) can replace the chocolate mousse.