Bûche de noël

Heat the oven to 180C/160C fan/gas 4. Butter a 32cm x 23cm swiss roll tin and line with baking paper. For the sponge, beat the egg whites in a large bowl using an electric whisk to stiff peaks. Whisk in 2 tbsp of the caster sugar.

In a separate bowl, whisk together the egg yolks and remaining caster sugar for 5 mins until pale and fluffy, and the whisk leaves a three-second ribbon in the mixture when lifted out. Sift in the cocoa powder and whisk until evenly combined. Add a third of the whipped egg whites to the chocolate mixture, stirring to combine and loosen the batter, then, using a large metal spoon, carefully fold in the remaining egg whites in a figure-of-eight motion so as not to knock out the air. Pour the mixture into the prepared tin, smoothing it using the back of a spoon. Bake on the middle shelf of the oven for 20-25 mins or until risen and a skewer inserted into the middle comes out cleanly. Cool in the tin for 5 mins.

Lightly dust a large sheet of baking paper with icing sugar, then invert the sponge onto it, cover with a clean tea towel and leave to cool fully. Once cool, carefully remove the tea towel and baking paper.

Meanwhile, make the filling. Whisk together the cream, sugar and vanilla bean paste until thickened but still spreadable.

For the topping, beat the butter until smooth, then whisk in the icing sugar and cocoa. Melt the chocolate in a heatproof bowl over a pan of simmering water (making sure the bowl doesn't touch the water) or the microwave in 20-second bursts. Cool slightly, then whisk the melted chocolate into the buttercream until smooth. Stir in 1 tbsp of boiling water from the kettle to loosen the buttercream, if needed.

Spread the vanilla cream filling over the sponge, leaving a 2cm border around the edge. Lift the longest edge of the cake up and over the filling to roll into a tight log, using the baking paper to help you. Transfer to a serving platter, then cut off the bottom quarter of the roulade on a diagonal and arrange it on the side so it looks like a branch on the log. Smooth the buttercream over the roulade using a palette knife, then use a fork to create lines for a wood-grain effect. Dust with icing sugar and decorate with redcurrants or fresh cranberries and holly or rosemary, if you like. Keeps in the fridge for up to three days.