If I’m after a quick, make-ahead dessert that works for a crowd, nine times out of 10 I’ll go for a no-bake cheesecake, because it’s so easy to put together and hard to mess up; it’s just a case of mixing and chilling. This one isn’t sickly-sweet and is brightened with the classic summery combination of lemon and elderflower. Build it in a square tin to make it go further, though it works just as well in a round tin.