Scotch whisky and apple are classic pairings, and here the apple comes in the form of calvados, with the richness of whisky liqueur balanced by tart, fresh...
Didn't know what to expect going in given the unorthodox list of ingredients, but the earthiness and light smoke of the scotch and the Drambuie harmonize perfectly with the fruitiness the passionfruit and calvados bring. "Rusty Nail meets Pornstar Martini" isn't a line that would've sold me on this, but it is an accurate description and it nevertheless works incredibly well.