My grammy passed her recipe for oatmeal cookies on to my mum, who wrote it down in her recipe book but says she could never make them ‘the same way’. It turns out Mum hadn’t written down the teaspoon of baking powder. She’d been making them for about twenty years without any leavening, ever since she moved from the US to London. After I eventually discovered the mistake and, given my inability to leave recipes alone, tweaked it, I ended up with these thin, crunchy cookies. They are quite different from the original ones but delicious all the same (and with the baking powder back in them!).