Very popular in Argentina where the combination of fernet & Coke is as much a staple as the G&T is in England. The drink is most identified with the Argentinian...
I really like this - I generally like the impact that Fernet brings to a cocktail. In this case, the Fernet still dominates (even though I use a 4:1 ratio) - but I really like how the cola dilutes the Fernet enabling you to taste some of the flavor notes a bit better. The strength of the Fernet still encourages you to sip slowly and gradually savor the cocktail - a nice drink to nurse.
With how much I've heard this drink raved about I was pretty disappointed. Eyeballed the coke but ended up adding a bunch more, maybe 4 or 5 parts to 1 part Fernet. Ended up adding some Angostura and a healthy squirt of saline which improved it a little but still... bleh