For the ganache, put the chocolate into a large bowl. Heat the cream in a pan until just boiling, then pour it over the chocolate. Leave for 5 mins, then stir until smooth. Put the ganache to one side to thicken and cool, then chill until needed.
For the caramel sauce, heat the sugar and butter in a pan until the sugar has dissolved and the butter has melted. Add the cream, bring to the boil, then remove from the heat and leave to cool.
For the brittle, line a baking tray with baking parchment, then put the sugar and 4 tbsp of water in a heavy-based frying pan and heat, without stirring, until golden brown. Stir through the nuts, and pour (in a thin layer) over the parchment. Sprinkle with ½ tsp flaky sea salt and leave to set.
To serve, drizzle each plate with sauce, heat a large spoon in a cup of hot water, then scoop out a curl of chocolate ganache for each plate. Break the brittle into shards and push a piece into each scoop. Sprinkle with crumbled brittle and add a pinch of sea salt.