Every kid in Britain probably knows about treacle tart, but for people in the USA it is a bit of a mystery. By bringing treacle into her books, J.K. Rowling introduces a treat with a long history. Treacle Tart is a traditional English dessert. It is made using a shortcrust pastrybase, with a thick filling made of golden syrup, also known as light treacle, breadcrumbs, and lemon juice. The tart is normally served hot or warm with a scoop of clotted cream, ordinary cream, ice cream or hot Birds custard. (we had some last night - just as a test - and it was yummy!)
Golden Syrup or light syrup, is a thick, amber-colored form of inverted sugar syrup, made in the process of refining sugar canejuice into sugar, or by treatment of a sugar solution with acid. It is used in a variety of baking recipes and desserts. It has an appearance similar to honey. It can also be used as a substitute for corn syrup.
Treacle Tart dessert is also featured in the movie Chitty Chitty Bang Bang. The childcatcher, in an attempt to lure out the children from the basement, calls out that he is giving away free sweets. His mention of free treacle tarts is the selling point for the boy, convincing him to be lured out into the street. "Treacle tart" is Cockney rhyming slang for "sweetheart".