Buche de Noel (Chocolate Chestnut Log)

First make the base by separating the eggs – put the whites in a large bowl and the yolks in a smaller bowl.

Then, using an electric hand whisk, whisk the egg yolks until they start to pale and thicken, add the sugar and continue to whisk until the mixture becomes more thickened (do not overdo this or it will go too stiff). Now whisk in the cocoa powder until it's thoroughly blended in. Next, wash the whisk heads in warm soapy water and, when they are absolutely dry, clean and grease-free, whisk the egg whites until they form soft peaks.  You can also watch how to separate eggs and whisk egg whites in our Cookery School Videos on this page.

Spoon one lot of egg white into the chocolate mixture to loosen it, then begin carefully to fold all the chocolate mixture into the egg whites, cutting and folding until they're thoroughly combined. Spread the mixture into the prepared tin, giving it a few taps to even it out, and bake it in the centre of the oven for about 20 minutes or until it is risen and puffy and feels springy in the centre – it's important not to overcook. When you take it out of the oven it will sink down quite a lot but that's quite in order, so don't panic. Let it cool completely, then place a sheet of silicone paper (baking parchment), about 1 inch (2.5 cm) larger all round than the Swiss-roll tin, on a work surface and sprinkle it with some icing sugar. Loosen the edges of the chocolate base all round, turn it out on to the paper and carefully peel off the base paper.

Now for the filling: simply empty the contents of the chestnut purée into a bowl, add 1 tablespoon double cream and mix thoroughly. Then, using a small palette knife, spread the mixture carefully and evenly all over the base. After that, sprinkle the chopped candied chestnuts all over. The next thing you need to do is have ready a plate that the whole length of the log will sit comfortably on (an oval meat plate can be used or you could line a small oblong tray with foil). Now, taking the edge of the silicone paper to guide you, roll the base over lengthways into a long roll, keeping it on the edge of the paper; then, transferring it to the plate, pull away the last of the paper. If it cracks or loses its shape don't worry: just pat it back into a log shape using your hands (nothing will show because of the topping). If you want to freeze it at this stage, keep it in the paper then wrap it in foil.

Now to make an authentic-looking log you need to cut two diagonal pieces off each end; these are to represent branches and should be about 2 inches (5 cm) at their widest part. Place one on one side of the log, cut side to join it, and the other on the other side but this time nearer the top. You'll find the sticky chestnut cream will make these two weld on to the rest okay. Now you have a log shape, all you require is some Christmas snow. For this you need to melt the chocolate in a bowl over some hot water, then beat the rest of the 10 fl oz (275 ml) cream till it's spreadable – be careful not to overbeat.

Now spread the cream evenly all over the log. Then drizzle a little trickle of melted chocolate up and down the length of the cream, take a fork and, working only lengthways, blend the chocolate lightly into the cream, giving a woody bark-like effect. The 'branches' need the chocolate swirled round with the fork at the ends, as do the ends of the log.

I also like to put fresh holly on the plate.