Preheat the oven to 200°C.
Melt the butter. Roll out the filo pastry and brush with the melted butter. Dust with icing sugar and cocoa powder. Place one sheet of pastry on top of another to create a double layer. Cut the filo pastry into 18 rectangles of equal size. Place the rectangles on to a baking sheet, cover with a sheet of baking parchment and then a second baking sheet. Transfer to the oven and cook for 6 minutes. Remove from the oven and allow to cool.
Bring the milk to the boil. Beat the eggs with 50g sugar until pale and fluffy.
Add the eggs/sugar to the milk and allow to thicken. Break the chocolate into pieces, place in a bowl and then add the milk/eggs/sugar mixture. Mix well until all of the chocolate has melted and you have a smooth chocolate cream. Add piment d'Espelette to taste then transfer to the fridge to cool and thicken.
Heat a frying pan and add the caster sugar. Melt, without stirring, to obtain a caramel. Once you have a dark caramel, add the salted butter and the cream. Mix well and allow to cool.
To assemble: place the chocolate cream in a piping bag. Pipe chocolate cream onto a filo rectangle, top with a second filo rectangle and then add another layer of chocolate. Finish with a third sheet of filo pastry and then drizzle over the sauce to finish.
«If you do not have any salted butter, use unsalted butter and add a pinch of fleur de sel to the caramel.»