For the meringue
- 150g/5¼fl oz free-range egg whites (approximately 5 egg whites)
- 300g/11oz caster sugar
- 2 tsp cornflour
- 1 tsp white wine vinegar
For the caramelised nuts
- vegetable oil, for deep frying
- 100g/3½oz caster sugar
- 100ml/3½fl oz water
- 110g/4oz mixed unsalted nuts
- sea salt flakes
For the filling
- 110g/4oz dark chocolate
- 500g/1lb 2oz sweetened chestnut purée
- 1 vanilla pod, seeds only
- 175g/6oz caster sugar
- 300g/11oz mascarpone
- 250ml/9fl oz double cream
- 8-12 marrons glacés (candied chestnuts), crumbled
For the caramel
- 150g/5¼oz caster sugar
- 1 tbsp water
For the meringue, preheat the oven to 140C/275F/Gas 1. Line a baking tray with greaseproof paper.
Whisk the egg whites in a clean bowl until soft peaks form when the whisk is removed.
Whisk in the sugar, a spoonful at a time, until all of the sugar has been added and stiff peaks form when the whisk is removed.
Whisk in the cornflour and vinegar.
Spoon the meringue mixture onto the baking tray in a large circle.
Bake in the oven for 10 minutes, then switch the oven off and leave in the oven for 2-3 hours, or preferably overnight, until crisp, but uncoloured.
Remove the meringue from the oven and set aside to cool completely, then place onto a serving plate.
Meanwhile for the caramelised nuts, heat the oil in a deep heavy-based frying pan until a breadcrumb sizzles and turns brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Heat the sugar and water in a separate saucepan until the sugar has dissolved.
Add the nuts and bring the mixture to the boil. Continue to cook until the temperature of the sugar syrup reaches 110C/225F (use a sugar thermometer to check this).
Remove the nuts from the syrup using a slotted spoon and carefully lower them into the deep fat fryer. (CAUTION: The nuts are coated in a liquid that may spit upon contact with the oil. Stand well back and keep your face and hair away from the deep fat fryer.) Fry for 1-2 minutes, or until golden-brown, then remove from the oil using a slotted spoon and set aside to drain on kitchen paper. Sprinkle with sea salt flakes.
For the filling, melt the chocolate in a bowl set over a saucepan of boiling water. (Do not let the base of the bowl touch the water.)
Smooth the melted chocolate over the cooled meringue.
Whisk the sweetened chestnut purée, vanilla seeds, caster sugar and mascarpone in a bowl until combined.
Whisk the cream in a separate bowl until soft peaks form when the whisk is removed. Fold the double cream into the chestnut mixture.
Spoon the chestnut mixture onto the meringue and scatter the marrons glacés and caramelised nuts on top.
For the caramel, heat a frying pan until hot, add the caster sugar and water and cook for 4-5 minutes, or until the mixture becomes a pale caramel. (Do not stir the mixture.)
Drizzle the caramel over the top to serve.