Preheat the oven to 210°C.
Line a swiss roll tin (33cmx22cm) or baking sheet with non-stick paper. put the eggs and sugar for the sponge into a bowl and whisk until smooth, light and fluffy. It’s best to use an electric hand whisk for this to get maximum aeration as it should triple in volume at least.
Sieve the flour and cocoa powder into the bowl and carefully fold in with a large metal spoon (avoid knocking out any air you’ve just whisked in.)
Spoon the mixture into the tin and carefully spread to the edges.
Bake for 10 minutes until the mixture springs back when lightly touched and it’s shrunk back from the edges slightly.
Lay another sheet of greaseproof paper on the table and sprinkle with a handful of castor sugar. Turn the hot swiss roll out onto the sugared paper, score a line 2cm in from one end and start to roll, allowing the paper to catch itself inside the roll. Leave to cool completely whilst rolled.
Make the butter cream icing by creaming together all the icing ingredients. Whip the cream to stiff peaks and fold through the alcohol (optional).
Unroll the sponge and spread the cream in a thin layer, right to the edges. Roll back up and reposition on whatever you intend to serve the Yule Log on.
Smear the chocolate butter cream all over and smooth into all the edges with a warm palette knife.
Run a fork through the cream to give the bark-like texture and draw rings around the end of the log with the melted white chocolate in a piping bag. Dust with icing sugar to represent snow.
Store in the fridge until needed and slice generously for everyone to enjoy. makes 12 slices.