So I've spent the last few hours deconstructing the Ink brush that Mike Schley used in his Lost Mine of Phandelver - Phandalin town map.
I've just posted a YouTube tutorial on how to create the brush and the necessary layer style that goes with it.

https://www.youtube.com/watch?v=zwCVla2y0Ck

Happy Mapping,

Eternal3lade