Triple chocolate Bûche de Noël

Preheat oven to 170°C (150°C fan) mark 3. Grease and line a 33 x 23cm (13 x 9in) shallow tin with baking parchment. Using a handheld electric whisk, beat
together egg yolks and sugar until pale, about 5min. Fold in the vanilla and  cocoa. In a separate bowl with clean beaters, whisk egg whites until stiff peaks form.

Using a large metal spoon, gently fold a third of the whites into the cocoa mix  to loosen. Fold in remaining whites until combined – be careful not to knock out too much air. Spoon into the prepared tin and level gently. Bake for 20min until the cake feels springy to the touch. Lay out a piece of baking parchment dusted generously with cocoa powder. Invert cake on to parchment and peel away paper from sponge. Leave to cool on a wire rack.

For the filling, whisk cream until it just holds its shape. Coarsely grate the white chocolate and fold into cream with the vanilla bean paste.

To make the topping, melt the milk and dark chocolate over a pan of gently
simmering water, making sure the bowl doesn’t touch the water. Set aside to cool. Whisk together butter and icing sugar until smooth. Fold through the  cooled melted chocolate.

Spread white chocolate filling over the cake. With the help of the paper, roll up the cake, working from a shorter side. Transfer to a plate. Spread buttercream over. Decorate with chocolate stars or glitter, if you like.