Preheat oven to slow 190oC/375oC/Gas
5. Grease, line and flour a 40 x 28cm Swiss roll tin.
Whisk the egg yolks with all but 25g
of the sugar until pale and thick. Add the vanilla essence.
Whisk the egg whites (with the cream
of tartar if not using a copper bowl) until they form soft peaks.
Add the reserved sugar and continue
whisking until stiff and glossy.
Fold half the flour into the yolk
mixture. Add a quarter of the egg whites and fold in to lighten the
mixture. Fold in the remaining flour, then the remaining egg whites.
Spread the mixture in the tin. Bake
for 15 minutes. Turn on to paper sprinkled with caster sugar. Roll up
and leave to cool.
Bring the cream to the boil. Put the
chocolate in a bowl and add the cream. Stir until the chocolate
has melted, then beat until it is fluffy and has thickened to a
spreading consistency. Mix a third of the chocolate cream with the rum
Unroll the cake and spread with the
rum mixture. Re-roll and cut off about a quarter, at an angle. Arrange
to form a branch. Spread the chocolate cream over the cake. Mark with a
fork, add Christmas decorations and dust with icing sugar.