Even at a modern speakeasy which otherwise eschews Vodka, you're likely to find a Moscow Mule served in a copper mug, for the simple reason that not only does it tend to be a best-seller, it also possesses 'Buck' lineage. And Bucks are drinks to be known and loved. Here's why.

There are a lot of complicated drinks to be had out there. Jiggers and precise measurements are de rigueur. But just as a Michelin-starred chef may fancy up a simple fast food taco, bartenders too need a break from all that mixology. Maybe it's a beer and a shot; maybe it's something so simple and foolproof that the jigger remains unsullied. Whatever it is, it needs to be quick and effective.
Welcome the Mule, or Buck as it's also known. There are those who will argue subtle differences between the Mule and the Buck, but practical application dictates that they are one-and-the-same - much like Mary Kate and Ashley Olsen. Do the minor differences really matter?
Mule Cocktail Recipe
1 Spirit of Choice (roughly 1 1/2 to 2 ounces (45 to 60 ml))
2 Half a lime or lemon
3 Ginger beer or ale
Add the spirit to a chilled collins glass filled two-thirds with ice. Squeeze in the citrus and toss in the shell as well and top with ginger beer or ale.
Mule to a host is what egg is to a chef
In the cocktail world, having a Buck in your arsenal is as invaluable as a chef having an egg on hand. What can't you do with it? Keep a couple of bottles of spirits, some ginger beer, and the odd citrus or two on hand and you'll be ready for just about any guests to walk through the door. Even if those guests happen to be the Olsens.