So...I thought about it for a while.
Currently chilling in my fridge, I've got an ATTEMPT at a Biscoff parfait. I took two 9" sponge cake rounds, sliced them horizontally into thirds (so I've got six centimetre-thick cake rounds), and layered them thusly--whipped cream with a bit of brandy, cake, biscoff spread, whipped cream, cake, custard, cake, biscoff and whipped cream, cake, custard, cake, etc.
I had to "wing it" a bit because I couldn't find biscoff, but I figured they were about halfway between a Pepperidge Farm "Bordeaux" cookie (one of my favorites, a butter-caramel crisp), and those light, delicate Belgian spice cookies, the kind that are about a millimeter thick. Wonderful things! I made a paste of those, coconut oil, a little sugar, a little cinnamon, a little vanilla.
The only real pressing problem I'm seeing is that the coconut oil freezes up in cold weather, so it's probably not the best choice to use in a parfait.
I've dumped the entire thing into a chamberpot for a serving dish, mostly because I didn't have any big round serving bowls...but also because I happen to have a chamberpot that I wasn't using, so to speak.
[Edit: Well, I'm not sure how to feel about the cake experience. It was a little busy - the cream of the whipped cream overwhelmed the custard, the custard wasn't very flavorful, which is sad, I love custard. But the cookies--well, the fact that the coconut oil set actually had an interesting side-effect, it made the spread crunchy and crisp, a bit like the original cookies were. So...in the balance, nto a bad experiment, but a little too complex to be worth repeating. If I'd let the overall thang chill overnight, it might have been more parfait-like, more blending of flavors and moist texture throughout, like a cinnamon-spice tirimisu. We'll see.]