These little cookies – described by one friend as tasting like a cookie within a cookie – are really a mixture between a meringue and a cookie. Hence they’ve become known at home, where they’re immensely popular, as Merookies, and are ideal with a cup of coffee after dinner. They are called “forgotten” as, just like the 'Forgotten Pudding' in Nigella Express, they are not baked, but put in a hot oven, which you immediately turn off, leaving the cookies to bake in the fading residual heat overnight. I find it all too easy actually to forget them, and always put a post-it sticker on the oven to remind me they’re in there, so I don’t burn them to a cinder by preheating the oven to cook something else in it the next day.
Preheat the oven to 180C/160C Fan/Gas 4 and line a large baking tray with baking paper. Whisk together the egg whites and salt in a grease-free bowl, 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/2in in diameter, onto the prepared tray. 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.
I always use ready-ground cardamom, as the amount you need is pretty much impossible to grind finely enough yourself (you’d need only an eighth of a teaspoon if using home-ground cardamom). And it is really worth seeking out mini chocolate chips, as I find regular-sized ones can spill out of the cloud-like mixture as you form them on the baking sheet.