Set the oven to 200°C or gas mark 6.
Whisk the egg whites with the lemon juice until stiff. In a separate bowl whisk egg yolks and caster sugar until thick and creamy then slowly add double-sifted cocoa and cornflour.
Beat one-third of the whisked egg whites into the cocoa mixture, then fold in the remaining whites using a metal spoon. Take extra care not to ‘knock’ the air out of the mixture. Spread evenly onto Swiss roll tin lined with greaseproof paper.
Bake in the centre of the oven for 7½ – 8 mins.
Whilst the sponge bakes, gets started on the creamy filling. Whisk the Lactofree® cream until it forms soft peaks, then whisk i the sugar and add brandy/vanilla if desired.
Once the sponge has been baked and cooled, turn it out onto a fresh sheet of greaseproof paper dusted with icing sugar. Lie the greaseproof paper on a clean tea towel to make it easier to roll.
Spread the cream mixture evenly over sponge, and roll up. Start at the short end and slowly, but firmly, roll – removing the paper as you go.
Once rolled, wrap in foil and refrigerate for 24 hours – you can skip this step but I would recommend placing the log in the fridge for a least an hour.
To serve, trim each end (the cooks treat!), dust with icing sugar and decorate as you please!