Just picking some of my favourites and must-reads for the pairing.
Easy Excercises, the fic that made me ship the pairing, and Love is a Verb that made it into my OTP. Part of the Feel the Fear universe that maps their relationship throughout history (also on AO3)
As I was going to St Ives, Out of Date and other Auld Alliance fics from the same author in the Sewn On universe
Grand Design that combines the aforementioned two series and contains two different versions of Scotland/France, related fic Dog Days and human AU Rookery Downs
Choux à la Crème - nsfw (also on Tumblr) and other fics from the author
Beautiful music - Backpipes vs. Accordion human AU, unfinished but updated