“Let them eat cake”.
The way I heard it, “cake” was kind of a translation error. It wasn’t sweet dessert. In those days the huge pans that bakeries used, would build up a layer of crud and carbon and was thrown away. The bums and vagrants would eat it. So when (or if) Ms. Antoinette said that, it wasn’t naive, it was pretty mean spirited.
I’ve heard that too.
“brioche” is sweet bread (not cake, not pastry either)
“pain” is bread. “pain perdu” = “lost bread,” what we call French Toast.