Boil 150g sugar and 300ml water to dissolve, simmer for 5 minutes, then chill overnight.
Soak dried cherries and cranberries in 90ml orange liqueur overnight.
Grease and line a 22cm loose-bottomed cake tin with paper.
Mix 300ml orange liqueur and the chilled stock syrup in a bowl.
Dip sponge fingers into the syrup and line the sides of the tin vertically.
Melt 150g chocolate in a bowl over a pan of simmering water.
Whisk 175g butter and 175g sugar together until pale and fluffy.
Fold in chestnut purée, melted chocolate, soaked fruit, and ground almonds.
Whisk 300ml double cream until thick and fold gently into the chocolate mixture.
Pour the mixture into the tin, cover, and chill in the fridge overnight.
Dissolve 350g sugar in 3 tbsp water in a heavy-based saucepan.
Heat the syrup to 155°C without stirring.
Plunge the pan base into cold water to stop the cooking process.
Flick the caramel over a rolling pin with forks to create sugar strands.
Turn the charlotte out and garnish with the spun sugar shapes.