I've never used apple syrup. Does it give them an apple-y flavour? I was wondering about using coconut nectar instead (which I already have). I'm also wondering about using a combo of ground almonds and coconut flour (and baking soda). Given that the spice is the predominant flavour, hopefully those changes wont take away from the character of the recipe.
Is this the single mixture amount or the double mix?
Hmm, I'm not sure how to describe the flavour to be honest. It gives them a 'full' flavour I guess, you really do notice the apple syrup in the recipe. However, if you don't have it, you can always switch it up with anything you have lying around, like more honey, other syrups or coconut nectar (never tried that myself). It shouldn't take away too much of the 'Pepernoten' flavour. I would definitely be interested in knowing how they'll turn out after you made the other switches! I think they'll still taste pretty good :-)
Good question, I'll add the answer to the article (It's the double mixture amount).