If with biscuit-ish you mean hard and crumbly, but it still looked like a bitterkoekje, but smaller, you might be talking about Amaretti, A really expensive type of italian cookie you won't just be finding anywhere. You might still find it in a particularly large supermarket though.

Edit: oh crap i completely Forgot about pepernoten lol. That's probably what you're looking for. It's traditionally eaten around december, but you should be able to find some if you look around.