White and dark chocolate yule log

Method

1. First, make the sponge. Heat the oven to 180ºC/160ºC fan/gas 4. In a large mixing bowl, beat together the eggs and sugar using an electric mixer for 4-5 minutes until the mixture is light and airy. Sift in the flour, cocoa powder, baking powder and a pinch of salt, then gently fold in with a large metal spoon until just incorporated.
2. Pour the mix into the lined tin, level out, then bake for 15-20 minutes until springy to the touch. Cool in the tin for 5 minutes, then turn out onto another sheet of non-stick baking paper, peel off the original sheet of baking paper and cool completely.
3. Meanwhile, make the dark chocolate buttercream. Put the chocolate in a heatproof bowl set over a pan of steaming, not bubbling, water (make sure the bowl doesn’t touch the water). Leave to melt, then set aside to cool for 5-10 minutes.
4. Put 100g butter in a large mixing bowl and beat with an electric mixer until soft, then gradually beat in the 130g icing sugar until completely incorporated. Add the melted dark chocolate and 90g apricot jam, then beat until slightly lighter in colour and aerated.
5. Put the sponge, still on its baking paper, on a large dinner tray or baking tray (to make it easier to transport), then spread over the 4-5 tbsp apricot jam, leaving 0.5cm or so around the edges. Top with the dark chocolate buttercream in an even layer- spread with a palette knife so it goes on evenly. Roll the sponge tightly into a log, starting from one long end, using the paper to help you. Turn the log so the seam is on the underside. Set aside while you make the white chocolate buttercream.
6. Put the white chocolate in a medium heatproof bowl set over a pan of steaming, not simmering water (make sure the base of the bowl doesn’t touch the water). Leave to melt, then set aside to cool slightly for 5-10 minutes.
7. Put the 200g butter in a large mixing bowl and beat with an electric mixer until soft, then add the melted white chocolate. Slowly whisk in the 80g icing sugar until completely incorporated and slightly lighter in colour. Spread a couple of teaspoons of the icing over the cake, including over the ends, so it just covers the sponge in a thin coating, then chill in the fridge for 20 minutes until the icing is firm.
8. Using a sharp knife, cut 5cm off one end at a 45 degree angle, then carefully place it on one side of the log at the end, so it looks like a stump leading off to the main branch. Spread the remaining icing over the top and around the sides to completely encase the log. Drag a fork over the icing in a loose pattern, so it looks like bark. Sift a small amount of icing sugar over the top just before serving, so it looks like snow.