As a bartender, I find [The Boulevardier] so useful because, with just the slightest tweaks, it’s transformed. It’s a great in its de facto form, but I often find Campari a bit of a bully to softer whiskies, even at the modern recipe’s half up ratio of 2 parts whiskey to 1 of Campari. By cutting the 1 part of Campari in half, or even thirds, one can swap in dozens of other amari, or what are known as potable bitters, and create new versions of the drink ad infinitum.
Case Study | The Boulevardier - NYTimes.com
Pretty much the same point I made about Negroni variations awhile back! The Negroni is a wonderful template.