Make them from waffle batter and deep fry the suckers.

Fill them afterwards of course.

Jam and flapjack are a terrible idea. Something thicker though, like caramel?

The bakery near my work actually does sell flapjack with a jam filling. I'm not entirely sure how they do that, whether they sliced it after baking and layered it, or whether they somehow did that before baking. I might try it sometime but the other stuff they sell like Kinder Egg Cookie Pies are difficult to pass up on, given that I can make flapjack myself.

For avoidance of doubt - where Daryil comes from flapjack is more like soft granola than pancake or whatever that term refers to in the USA.