Considering how revered the stack cake is/was in parts of the Eastern U.S., there’s surprisingly little written about it. It’s been said that the stack cake was brought to (what is now) Kentucky by way of Pennsylvania, by one James Harrod, in the late 1700’s. That theory has a certain appeal, since Germans were pouring into Pennsylvania at the time, and it’s a least theoretically possible that some of these immigrants knew about torte-style cakes, and perhaps even baked a few, assuming they could lay their hands on the ingredients.
The problem with this theory is, first, that James Harrod wasn’t German. He was from a British family. Second, he was a frontiersman, a contemporary of Daniel Boone and George Rogers Clark, known for hunting, fishing, trapping, and rifle skills. From a very young age (possibly as young as 14) he served as a Revolutionary-era militiaman, and afterward spent most of his time in the woods leading expeditions, living with Indians, and learning Indian languages.
That’s not a profile of a pastry enthusiast, at least to my mind. But who knows? He may have whiled away the evenings in front of his camp fire dreaming of cakes. But even assuming that’s true, there’s a further problem. Harrod died in 1792, which is almost a full 100 years before the Kentucky area’s first flour mills were built. Prior to that time there would have been no wheat flour available anywhere west of the Alleghenies. The staple starch would have been corn (i.e. corn meal) which doesn’t bake up into cakes very well.
So I think the only conclusion we can come to is that the stack cake was a home-grown innovation, dating from the late 1800’s or early 1900’s, about the time home baking was becoming popular everywhere else in the US. Lacking ovens and baking forms, it makes sense that mountain bakers would have simply used skillets, griddling their thin wheat-flour layers over (or beside) a hearth fire. Nothing else would have been possible technically, at least nothing that I can think of.
In short, I think stack cakes were simply a blend of old techniques with new ingredients — and new aesthetics. Despite what a lot of us think about mountain people, they aren’t cut off from mainstream American culture, and never really have been. People living in Appalachia, even in the late 1800’s, would have heard about and seen the layer cakes that were being made everywhere else in America, and, I expect, would have done their best to replicate them with the equipment and ingredients they had on hand.