50 g (2 oz) shop-bought thick, fresh crème pâtissière or vanilla custard
beaten egg, for brushing
50 g (2 oz) plain dark chocolate chunks or chips
50 g (2 oz) pistachio nut kernels
4 teaspoons granulated sugar
2 tablespoons icing sugar
1–2 teaspoons milk
Line a large baking sheet with nonstick baking paper. Unroll the pastry and cut in half widthways to make 2 rectangles. Place each pastry sheet so that the short edge is facing you, then lightly score the surface lengthways into equal thirds.
Spread the custard evenly over the middle third. Cut the outer thirds of pastry into diagonally slanted strips about 1.5 cm (3/4 inch) thick, then brush with beaten egg. Scatter the chocolate chips and two-thirds of the pistachios over the custard, then bring the pastry strips over the filling, alternating the sides to create a plaited effect.
Roughly chop the remaining pistachios. Brush the pastries with beaten egg, then sprinkle with the chopped pistachios and granulated sugar. Place on the prepared baking sheet and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 18–20 minutes until golden and puffed.
Meanwhile, mix the icing sugar with just enough milk to create an icing of drizzling consistency. Remove the pastries from the oven, drizzle over the icing and transfer to wire racks. Cut each pastry in half and serve warm or cold.