Gin, curaçao, lime, and bitters. Not to much look at, you might think, but wow, what a dream in a glass. Some recipes call for just Angostura. Better recipes (in my opinion) ask for both Ango and orange bitters. The addition of the orange helps to marry the citrus flavors present in the gin, lime, and curaçao.
Corpse Reviver #2
The Corpse Reviver #2 is the drink I most regret leaving off my original list of essential cocktail everyone should know. Originally, corpse revivers were a class of cocktail, all intended to serve as hair-of-the-dog remedies for hangovers. Only two of this family of drinks survive, and of them, only one is notable. The Corpse Reviver #1 is okay, I guess: cognac, apple brandy, and sweet vermouth. It's a rich, boozy drink, but it lacks depth and complexity.
Number Two, though, doesn't suffer that fate. Gin, Lillet, lemon juice, and Cointreau, with a teeny amount of absinthe—it's a complex, layered, and balanced drink. The citrus flavors from the lemon and the orange liqueur are refreshing enough to make this a brunch drink, and of course, that's probably when you'd want a hair-of-the-dog anyway.
The Improved is a variation on the Old Fashioned, but I'm including it here for a couple of reasons. First, it's an excellent variation on an OF, and it illustrates the principle that even a small change to a cocktail can make a whopping difference to the flavor of a drink. Second, the Improved is something of a bridge cocktail between the OF and another drink on my original list. Let me explain.
Remember, the original cocktail called for spirit, sugar, water, and bitters: that's it. You made it by dissolving the sugar into the water, adding the spirit and bitters, and stirring. This became the basic template for the Old Fashioned. Bartenders then branched out, subtly, from there. If you took that original cocktail and rubbed a piece of lemon peel around the rim of the glass, that was a Fancy cocktail. If you took the original and added a hit of curaçao or maraschino liqueur to it, you had an Improved.
But say you make three subtle changes to the Improved. Instead of mixing the liqueur into the drink, you swirl it around the inside of the glass and then discard it. Instead of maraschino or orange liqueur, you use absinthe. And instead of Angostura bitters, you use Peychaud's. Well, then: Sazerac.
Now, I tell you all this, but I don't believe that an Improved Whiskey Cocktail is really all that preferable to an OF or a Sazerac. Give me a choice, and the Improved will always be third on my list. (Whether I'm going for the OF or the Saz simply depends on my mood, how physically close I am to the French Quarter, and how temporally close I am to Fat Tuesday.)
No, what you really want to try is an Improved Gin Cocktail, made with genever. The maltiness of genever is enhanced by the other ingredients, and you wind up feeling like you're drinking a weird but pleasing blend of gin and malt whisky.
On my initial list of 25 cocktails everyone should know, there's nothing I'd eliminate to include the Mojito, but given space for five more, I think it would be silly not to include it. The Mojito is sparkling enough to be refreshing but still boozy enough to make you know you're drinking. Mint, lime, and rum simply taste smashing together. As my correspondents point out, it's the national drink of Cuba, and a nation that's contributed so much to drinking culture has to know a thing or a hundred about booze. So, here's your Mojito. Cheers.