I honestly don’t know the answer to that, but I do know this: if you’re lucky enough to find it in France, do yourself a favor and get it. But here’s the deal: it’s called pain perdu (literally “lost bread”) and it’s not on the breakfast menu. It’s a dessert, baby. I like mine with ice cream. And whipped cream (chantilly). And mint.
So where did French toast originate? I’ll let the food historians sort that one out. I just know that when I get some, it doesn’t last long.