250 g butter, plus extra for greasing
250 g dark chocolate, broken into chunks
250 g unsweetened chestnut puree
250 ml milk
125 g caster sugar
1 tsp vanilla extract
4 eggs, separated
300 ml whipped cream
A handful of redcurrants or raspberries
Heat the oven to 160c/fan 140c/gas 3 and lightly grease a 23cm springform cake tin.
In a saucepan, gently heat the dark chocolate, chestnut puree, milk, sugar, vanilla extract and butter.
Stir until smooth and melted, but by no means boiling.
Remove from the heat. In a bowl, beat the egg yolks and then stir them into the chocolate mixture.
Next, whisk the whites until stiff but not dry and gently fold them in.
Pour the whole mixture into the cake tin and bake for 40 minutes or until the top looks firm but still has a little wobble in the middle.
Cool the cake in the tin, then remove with care.
When ready to serve, top with the whipped cream and red fruit.