Show of hands here: How many of you have been inveigled by a perverse bartender into trying a straight shot of Fernet-Branca? And your reaction? Thought so.
Fernet (there are other formulations besides the Branca label) is one of a class of Italian bitter digestivos called amari, plural of amaro and a word putting it all out there: bitter. Though they are produced in many countries, these multi-herbal alcoholic concoctions are especially popular in Italy. They may have originally arisen as tonics designed to settle the stomach after a tad too much spaghetti, but today are also the darlings of the shaker set.
If you want to explore mundo amaro (and, the forgoing notwithstanding, I think you should), I suggest you start somewhere lower on the totem pole than Fernet—unless, of course, you are one of those genetically lucky people that can't, in any but high concentrations, taste aloin, the bitter component in aloe that gives Fernet much of its "bracing" quality. Says Amy Stewart, author of The Drunken Botanist, "If bitterness had a color, aloe would be black as coal."
Many of us already are familiar with Campari, now better known as an aperitivo mixed with soda or as a component, with gin and sweet vermouth, in the popular Negroni cocktail; it's a good place to start. Its color is perversely seductive (and was once derived from the cochineal bug), and though the secret (of course) blend of bitter tree bark and herbs infused in alcohol is certainly bitter, it doesn't hold a candle to Fernet. Aperol, with its mix of bitter orange (it comes through in the nose), gentian, rhubarb and more secret stuff, also considers itself an aperitivo. It's a touch sweeter than Campari, is also good with soda and is essential in the Intro to Aperol cocktail with gin, lemon juice, simple syrup and Angostura—one of those other accent bitters.
Sweeter, but deeper and now definitely in the digestivo camp, is Averna. This one I can easily do straight or on the rocks, but it is also good in a drink such as the Vertigo in which two ounces are mixed with half an ounce of lemon juice in a glass of ice to which ginger beer is added as a topper. Amaro Nonino Quintessentia is grappa-based and admits to cinchona bark, among other ingredients. Amongst the amari on my bar, this is perhaps my favorite—bracingly bitter but not ball-bustingly so. It's also necessary to the appealing Paper Plane (Google it). Other names to look for are Braulio and Ramazzotti.
So now it's time to admit that I did buy a bottle of Fernet-Branca as a kind of anti-aversion therapy—just a little at a time, genes willing. I'm not there yet (so I guess that means no knocking back shots with off-duty 'tenders at 2 a.m.), but I do recognize the importance of F-B in cocktails such as the frisky Hanky Panky, a riff on the Negroni. In varying proportions, you could try subbing in any of the above, as well.