Prue Leith reckons the custard cream is “arguably Britain’s most iconic biscuit” – and, certainly, we’ve been dunking this fern-patterned treat in our tea for well over a century, with early advertisements for this “delicious biscuit” placing it, perhaps aspirationally, in the “fancy” category. By 1920, Bermondsey baking behemoth Peek Frean could confidently declare the custard cream “far and away the most popular of all the cream sandwich biscuits”, a status only slightly dented by the time I was at school about seven decades later, when it sat just below its contemporary, the chocolate bourbon, in the playtime snack ratings. Despite my love of both custard and cookies, however, I’ve always found this particular custard-flavoured product a bit sugary and dull.…