Preheat oven to 200C and grease and line a swiss roll tin
whip the eggs and sugar till they double in volume
sieve the flour and cocoa powder and fold this into the egg mixture with a metal spoon
Pour cake batter into prepared tin and bake for approx 10 minutes till it bounces back when you touch the centre
Tip the cake on to a new piece of baking parchment and peel off the old paper
score a line on short edge and use baking parchment to roll the cake then leave it to cool
Filling
Whip sugar and cream till you get soft peaks
Frosting
Beat all the ingredients together
Assembling the cake
Unroll the sponge and spread with the cream then roll up putting open end down on serving plate
Cut a thick diagonal slice from one end of the cake and place this against side of cake to create a V branch
Cover the whole cake in the chocolate frosting and make surface rough like bark by running over it with a fork
Sprinkle with some extra icing sugar like snow and add holly etc to decorate
Notes
You can use grated chocolate on top of the frosting or make strips of chocolate using a potato peeler from a bar of either milk or plain chocolate (or both for a nice textured look) and scatter these on top of the frosting.