Preheat the oven to 170°C/fan 150°C/gas 3. Butter a shallow 33 x 23cm rectangular baking tin and line it with baking parchment.
Put the eggs and sugar into a large mixing bowl (or the bowl of a food processor), then use an electric hand whisk to beat for about 7 minutes, or until the mixture is thick enough to leave a ribbon trail when the whisk is lifted out. Now sift the flour and cocoa over the egg mixture. I don’t normally think you need to sift flour, but in this case, because we’re dealing with a delicate mousse, you really must. Gently fold them both in. The mixture will lose volume, but you need to try and get the flour and cocoa incorporated as quickly as possible without knocking out the air. Pour into the prepared tin and bake for 12 minutes, or until the mixture bounces back when lightly touched in the centre. Turn the cake out on to a sheet of baking parchment and leave to cool for 15 minutes.
For the filling, you need to make a dry caramel. This is sometimes considered quite a tricky way to make caramel, but I have fewer mistakes making it this way than any other. The trick is to let the caramel cook very slowly and evenly, and you must never stir the pan until all the sugar has melted. Place the sugar in a frying pan and slowly melt it over a medium heat – this will take about 8 minutes. You can shake the sugar around the pan, but never stir it. By the time the sugar melts it will have started to turn a rich golden colour. When it hits a deep mahogany and has tiny imploding bubbles on the surface, quickly whisk in the butter, the 50ml of double cream, vanilla extract and salt. Toss the chestnuts though the caramel, then, while they are still hot, blitz in a food processor or blender until smooth. Whip the 150ml of cream until it forms soft peaks, then fold in the chestnut purée mixture.
To make the icing, place the cream, butter and chocolate in a small pan and heat gently, without boiling, stirring until the chocolate has melted. Remove from the heat and stir until smooth, then leave until cold. Chill for 30 minutes, then beat with a whisk until it thickens up to become a really smooth, glossy paste. Spread the chestnut cream over the top of the cake. Roll the cake up to form a log shape and place seam side down on a serving plate. Spread the icing over the top and sides of the cake and smear it into the texture of a log. Scatter the crumbled chocolate flakes over the icing, decorate with a stalk of redcurrants (or whatever you choose) then lightly dust with icing sugar to finish.
For the Cake
- unsalted butter, to butter the tin
- 3 large free-range eggs
- 75g caster sugar
- 50g plain flour
- 25g cocoa powder
For the Filling
- 100g caster sugar
- 1 x 200g vacuum-pack of readycooked, peeled chestnuts
- 80g unsalted butter
- 150ml double cream, plus 50ml for the caramel
- 1 teaspoon seeded vanilla extract
- ¾ teaspoon salt
- 150ml double cream
- 30g unsalted butter
- 150g dark chocolate
- 2–3 chocolate flake bars, crumbled
- icing sugar, for dusting
- a stalk of redcurrants or other Christmas decorations such as holly or figurines
Recipe and photographs are from Season’s Eatings by Gizzy Erskine, with photography by Emma Lee, published by Mitchell Beazley, RRP £15.