I've been making dutch apple pastries for a couple of weeks now, and I've noticed that the apple filling that spills from the pastries turns dark brown like apple syrup (or apple butter, apple paste or apple cheese) The taste is similar, as well. But the texture is off.  The question is how to make a real batch of apple syrup? Apple, sugar & heat for some amount of time? Or are some other ingredients needed? 
I admit, I've never attempted making stroop (apple or otherwise) on my own ... but some discussion on a forum post regarding Dutch cooking mentioned that there's something called 'apple cheese' which sounds like it might be quite similar, based on the description of the end consistency and the amount of sugar used. 