125g/4½oz good quality dark chocolatebroken into chunks
85g/3oz butter
1egg plus 2 yolks
3tbspcaster sugar
Instructions
To make the pastry, put the flour, cocoa and butter into a food processor and whiz until the mixture looks like breadcrumbs. Add the sugar and whiz again. Mix the egg yolk with the water and add that. Process again until the mixture comes together in a ball. You may need to add a little more water. Wrap in cling film and leave to rest in the fridge for half an hour. Roll out the pastry on a lightly floured surface and use to line a deep 24cm (9 in) tart tin with a removable base. Carefully trim the excess from the rim and keep to patch up any holes later on. Put in the fridge or freezer to chill until firm. Preheat the oven to 200ºC/400ºF/gas mark 6.
To make the caramel, put the sugar and water into a heavy-bottomed saucepan. Heat slowly so that the sugar dissolves. Once it has, turn up the heat and boil until the syrup turns to caramel – you will know by the smell and colour. Be careful not to take it too far and burn it. Once it has reached the caramel stage, stir in the cream – stand back as it will hiss and spit – and the butter. Add the salt and stir to help everything to melt and blend. Leave to cool.
Prick the base of the tart case, line with greaseproof paper or foil and fill with baking beans. Bake blind for 12 minutes, then remove the paper and beans and leave to cool a little. Pour in the caramel. Turn down the oven to 180ºC/350ºF/gas mark 4.
To make the filling, melt the chocolate with the butter in a bowl over a pan of simmering water. Remove and leave to cool a little. Whisk the eggs and sugar using an electric beater until the mixture is light and fluffy and has increased in volume. Stir in the chocolate and butter. Pour over the caramel and put in the oven. Bake for 12 minutes. Leave until cool enough to handle, then carefully remove the rim and put the tart on a plate. Decorate with a very light scattering of sea salt flakes and serve.