Review:

Spirituous and just on the sour side, the sugar rim is considered by some to be integral to this classic cocktail. Dilution is key to perfecting a Sidecar, so if using ice straight from a freezer (rather than an ice machine), consider adding 10 to 15ml chilled water. In place of a sugar rim, some may want to add 2.5ml or more sugar syrup or see my Sidecar recipe.

Variant:

Difford's Sidecar recipe
Sidecar Royale - a Sidecare charged with sparkling wine/champagne
Apple Cart - a calvados-based Sidecar
Biblical Sidecar - a spicy Christmassy sidecar
Biggles Sidecar - with ginger liqueur
Chelsea Sidecar - gin-based
Chocolate Sidecar - with crème de cacao and port
Eastern Raspberry Sidecar - with sake and fresh raspberries
Gennaros Sidecar - with limoncello
Grand Sidecar - Difford's two-ingredient Sidecar
Lady's Sidecar - with orange and lemon juice
Champs-Elysees
Marignay

History:

In his 1948 Fine Art of Mixing Drinks, David A. Embury says of the Sidecar's origin: "It was invented by a friend of mine at a bar in Paris during World War I and was named after the motorcycle sidecar in which the good captain customarily was driven to and from the little bistro where the drink was born and christened."

Embury doesn't name the bar, but it's commonly assumed that he meant Harry's New York Bar and that its owner, Harry MacElhone, created the cocktail. However, in his own 1922 ABC of Cocktails, Harry credits the cocktail to Pat MacGarry, "the Popular bar-tender at Buck's Club, London." However, in later ABC of Cocktails editions, he appears to take credit for the cocktail himself. The fact that MacElhone worked alongside Malachi "Pat" MacGarry at Buck's Club when it first opened just a few years earlier in June 1919 may have some bearing on this.

MacGarry being the originator of the Sidecar is further reinforced by the first printed recipe appearing in Robert Vermeire's Cocktails How To Mix Them, published in May 1922, just a few months before Harry MacElhone's ABC of Cocktails.

Side-Car.
Fill the shaker half full of broken ice and add:
1/6 gill of fresh Lemon Juice.
1/6 gill of Cointreau.
1/6 gill of Cognac Brandy.
Shake well and strain into a cocktail-glass.
This cocktail is very popular in France. It was first introduced in London by MacGarry, the celebrated bar-tender of Buck's Club.

Robert Vermeire, 1922

Like so many classic cocktails, we will probably never know who created/named the Sidecar cocktail, but it appears to have been created by MacGarry in London and then popularised by Harry MacElhone at his Parisian bar.

In the 1938 French-language version of his book, Vermeire adds weight to French adoption claims by stating that the south of France was the drink's home. Before anyone suggests it, there is no evidence to support the Sidecar being "invented at the Carlton Hotel in Cannes."

Nutrition:

One serving of Sidecar contains 172 calories