Fascinating little drink! I made with a ristretto shot drawn from a super-automatic machine, using Lavazza Super Crema (which I believe is a blend of arabica and robusta beans). Appleton 8 yr. Much more subdued than a shot of ristretto should be - it is nutty, with a bit of lemon nose when sipping (but not in the taste). Not sweet, and only a bit bitter (again, much more subdues than a ristretto shot). Excellent!
As a note, don't use your artisanal coffee for this. If it incluses words like "single origin" or "high grown" or whatever, it is not optimal here.
You want a classic, high roast level, "commercial" style where nowhere it utters the label "100% arabica".
You know what I mean here.
With such a robust coffee, this pleasantly balances the bitterness and brings interest, while those lighter, more fruity and acidic blends would throw the balance off.