Preheat the oven to 200C/400F/Gas 6. Lightly greasea 33x23cm/13x9in Swiss roll tin, and line with non-stick paper or bakingparchment, pushing it into the corners.
For the sponge, in a large bowl whisk the eggs andsugar using an electric hand whisk until the mixture is pale in colour, lightand frothy. Sift the flour and cocoa powder into the bowl and carefully cut andfold together, using a spatula, until all the cocoa and flour are incorporatedinto the egg mixture. (Be careful not to beat any of the air out of themixture).
Pour the mixture into the lined tin and spreadevenly out into the corners. Bake in the middle of the preheated oven for 8–10minutes, or until well risen and firm to the touch and the sides are shrinkingaway from the edge of the tin.
Place a piece of baking parchment bigger than theSwiss roll tin on the work surface. Dust with icing sugar generously. Carefullyinvert the cake onto the paper and remove the bottom lining piece of paper.
Cut a score mark 2.5cm/1in in along one of thelonger edges. Starting with this edge, begin to tightly roll up the spongeusing the paper. Roll with the paper inside and sit the roll on top of itsoutside edge to cool completely.
While the cake is cooling, make the ganache topping.Heat the cream in a pan, just so as you can keep your finger in it. Remove fromthe heat and add the chocolate, stirring until it is melted. Cool to room temperature,then put into the fridge to firm up (this icing needs to be very thick forpiping).
Uncurl the cold Swiss roll and remove the paper.Spread the whipped cream on top, and re-roll tightly. Cut a quarter of the cakeoff from the end on the diagonal. Transfer the large piece of cake to a servingplate and angle the cut end in to the middle of the large cake to make abranch.
Put the chocolate icing into a piping bag fittedwith a star nozzle. Pipe long thick lines along the cake, covering the cake completelyso it looks like the bark of a tree. Cover each end with icing or, if you wishto see the cream, leave un-iced. Alternatively, just use a palette knife tospread on the icing and create rough bark texture with a fork.
Dust with icing sugar and garnish with fresh hollyor a little robin to serve.
