Preheat the oven to 180°C/160°C Fan/350°F. In a grease-free bowl, whisk together the egg whites and salt until you have soft peaks. Whisk in the sugar a little at a time until thick and gleaming.
By hand, fold in the cornflour, vinegar and cardamom, then add the chocolate chips and most of the pistachios and very gently fold these in too.
With a spoon, drop mounded blobs of the mixture, 4-5cm / 1½-2 inches in diameter, onto a large baking sheet lined with baking parchment. Sprinkle with the remaining pistachios.
Put the cookies into the oven, shut the door and turn off the oven immediately. Let the cookies sit in the turned-off oven overnight.
