A CENTURY AGO THE COCKTAIL ACHIEVED PERFECTION when, according to legend, Count Camillo Negroni asked his bartender in Florence to stiffen an Americano by replacing the soda water with gin. The world never looked back. With its cosmically simple 1:1:1 ratio, its balance of bitter and sweet, its pleasant kick, its aura of sophistication, the Negroni has bewitched cocktail lovers ever since. Perhaps none more so than Matt Hranek, who intones this love song to his favorite drink and offers a curated collection of recipes, both the classic and dozens of variations, deviations, and delicious reinterpretations.