• For the Sponge
• Pre-heat your oven to 425 F / 220 C / Gas Mark 7 and butter and line a 20cm x 30cm baking tray with baking paper.
• Place the eggs into a large bowl and add the sugar and vanilla. Whisk the eggs and sugar together until pale and very thick. You can do this by hand or use an electric mixer.
• Using a metal spoon gently fold in the flour, cocoa and salt until thoroughly incorporated with no streaks or pockets of flour left.
• Gently transfer the sponge mix into the tin and spread to the corners. Bake for eight to ten minutes until cooked and springy to touch.
• Set the cake aside and cut a piece of baking paper slightly larger than the sponger. Scatter with caster sugar and using a folded, dry tea towel carefully flip the baking tray and tip the sponge onto the baking paper.
• Lift off the baking tray and peel of the baking paper on now on top of the sponge. Lift the bottom layer of baking paper at one end and paper roll the sponge with the paper running through it and allow to cool.

For the Chocolate Buttercream

• Sift the icing sugar and cocoa into a large bowl and add the butter, beat together with a wooden spoon or electric mixer. Heat the milk until scalding in a microwave and in a jug, mix in the vanilla and stir until it is all combined and allow to cool.
• Gradually pour the cold milk and vanilla into the icing while mixing on a slow speed, then turn the mixer up to a high speed and beat the icing until light and fluffy.
• When the sponge is totally cool, unroll and spread over a third of the icing, leaving a three-centimetre strip clear. Starting from the clear trip of sponge, use the baking paper to roll the sponge back up again around the filling.
• Transfer onto a cake board or plate and cover with the remaining icing. Using a fork score the icing to look like tree bark, decorate if desired and dust with icing sugar.