Method

Preheat the oven to 180°C/350°F/gas mark 4. Line a shallow 30.5cm x 20.5cm (12in x 8in) Swiss roll tin with oiled tin foil or parchment paper.

Separate the eggs. Put the yolks into a bowl, gradually add the caster sugar and whisk until the mixture is thick and pale lemon coloured.

Melt the chocolate with the water in a saucepan set over a very gentle heat, then set aside while you whisk the egg whites to firm snow.

Add the melted chocolate to the egg yolk mixture. Stir a little of the egg white into the mixture, then cut and fold the remainder of the egg whites into the mixture and turn it into the prepared tin.

Bake in the preheated oven for 15–18 minutes, until firm to the touch around the edge but still slightly soft in the centre.

Wring out a tea towel in cold water. Take the roulade out of the oven and let it cool slightly, then cover with the cloth. (This is to prevent any sugary crust from forming.) Leave it in a cool place. Provided the cloth is kept damp, it will keep for 2 days like this.

To serve, whip the cream and flavour with the rum. Put a sheet of grease-proof paper on a table and dust it well with sieved icing sugar.

Remove the damp cloth from the roulade and turn the tin upside down onto the prepared paper. Remove the tin and carefully peel the foil off the roulade.

Spread with the rum-flavoured cream and roll it up like a Swiss roll. Cut about one-third off the roll at an angle.

Lift the roll onto a serving plate, arrange the smaller piece so that it looks like a branch and dust well with icing sugar.

Decorate with Christmas cake decorations, such as holly leaves, Santas or robins, sprinkle again with a little extra icing sugar and serve.