Line a baking tray with baking parchment. Unroll the pastry then turn so one of the longest sides is towards you, and imagine you’re going to fold it in half like closing a book. Mix the custard with the ground almonds.
Spread the custard mixture over one half of the pastry, then scatter over the chocolate chips and chopped pistachios. Fold the other half of the pastry over the top. Cut into 6 strips, so each one has the fold at one end. Gently twist each strip a few times – this bit can be messy! Space the twists on the prepared tray, then put in the freezer for 30 minutes. Preheat the oven to 220°C (200°C fan oven) Gas Mark 7.
Sift the icing sugar over the twists and scatter with a few more chopped pistachios. Bake for 15-20 minutes until golden and crisp. Enjoy with a lovely cup of coffee.