250g/9oz plain flour, plus extra for dusting
1 tbsp demerara sugar, for sprinkling
50²µ/1¾´Ç³ú roasted hazelnuts, chopped
25g/1oz icing sugar, plus extra for dusting
½ tsp salt
100²µ/3½´Ç³ú dark chocolate (minimum 70% cocoa solids)
250g/9oz very cold unsalted butter, cut into cubes
200ml/7fl oz double cream
50²µ/1¾´Ç³ú mascarpone
2 tbsp instant coffee, mixed with 1 tbsp boiling water to make a paste
1 free-range egg, beaten for egg wash