Shake once without ice and once with ice, strain into a single old fashioned glass or a cocktail coupe, and garnish with freshly grated nutmeg.
I also made a lighter variation using Cynar instead of Fernet that worked well too. See source reference link for more information on that. Also, I was unaware of Kindred Cocktails' Applejack's creation of the same name but took things in an absinthe instead of Campari direction.
Every once in a while when I have bar guests at Drink who want weird cocktails, I opt for Ted Kilgore's Industry Sour which is essentially a Fernet-Chartreuse "Daiquiri." Also in that vein is the Campari-Chartreuse Love & Murder, and I wondered if I could mash up these three elements into a Flip (also the Ferrari of Fernet-Campari connects the trilogy). Paying tribute to the inspiration, I dubbed it the Industry Flip.