Review:

A Clover Club freshened and made more interesting by the addition of fresh mint, and not just as a garnish.

Variant:

Clover Club
Clover Club (Difford's recipe)
Clover Club (Julie Reiner's House-Made)
Clover Leaf Martini

History:

The Clover Leaf is ostensibly the same as the Clover Club, with various similar recipes coexisting since 1909. The commonly accepted difference between these two very similarly named cocktails comes from Harry Craddock's 1930 The Savoy Cocktail Book where he states a Clover Leaf Cocktail is "The same as Clover Club, with a sprig of fresh Mint on top" and so for most it is merely the decoration that distinguishes the two cocktails apart. However, there's a little more to it than that.

The first known recipe for Clover Leaf appears in Jacob Abraham Grohusko's 1908 Jack's Manual, while the first Clover Club is found in Paul E. Lowe's 1909 book Drinks: how to mix and how to serve. [The Oxford Companion to Spirits And Cocktails references a 1901 Clover Club recipe published in the New York Press on 21st June 1901, but I haven't been able to validate this.]

A CLOVER LEAF
In genuine old fashioned American hot weather nothing seems to tickle the palate like a good American drink, and
the kind selected generally indicates the characteristics of the person drinking. In winter a man will take almost anything that happens to be the fad for the moment, whether highly flavored or not, but in summer the demand is for something that will quench the thirst, whether beer, lemonade or gin rickey or some other beverage. The Clover Leaf is said to be popular in the city of brotherly love. Certainly it is decorative, for it has a soft orchid color, with a rim of white.

Drink is made of:
½ teaspoonful of sugar
100% Gordon gin
10% raspberry syrup
White of an egg
1 sprig of mint.
Fill glass with cracked ice, shake well, strain in champagne glass and serve.

Jacob Abraham Grohusko, Jack's Manual, 1908

The Clover Leaf is also reported as being "a new appetizer" in the New York Herald on the 8th July 1908, and as with Jack's Manual, says it's "popular in the city of brotherly love", a reference to Philadelphia which is coincidentally where the Clover Club was founded in 1896, met.

A party of Philadelphians introduced a new appetizer at the Plaza last evening called a clover leaf cocktail. It is said to be popular in the city of brotherly love. Certainly it is decorative, for it has a soft orchid colour, with a rim of white, and is served in glasses with round bowls. The drink is made with Gordon gin, raspberry syrup. White of an egg and a bit of mint, shaken well with ice and drained off.

New York Herald, 8th July 1908

While the Clover Club is omitted from Grohusko's 1908 first edition, his third 1910 edition is the earliest cocktail book to carry recipes for both a Clover Club and a Clover Leaf. This may strengthen the argument that the Leaf predates the Club but more importantly, the 1910 edition handily defines the difference between the two cocktails – both are gin-based with egg white, and mint, but the Clover Leaf is sweetened with grenadine while the Clover Club uses raspberry syrup and additionally has lime, lemon and orange juice. [Both recipes also appear in his 1910 second edition but confusingly he names both recipes Clover Leaf – let's assume this was a simple naming error!]

CLOVER CLUB COCKTAIL
White of 1 egg
Juice ½ lime
Juice ½ lemon
Juice ½ orange
1 tablespoon raspberry syrup
100% dry gin
1 sprig fresh mint
Fill glass with broken ice, shake, strain and serve.

CLOVER LEAF COCKTAIL
In genuine old-fashioned American hot weather nothing seems to tickle the palate like a good American drink, and the kind selected generally indicates the characteristics of the person drinking. In winter a man will take almost anything that happens to be the fad for the moment, whether highly flavored or not, but in summer the demand is for something that will quench the thirst, whether beer, lemonade or gin rickey or some other beverage. The Clover Leaf is said to be popular in the city of brotherly love. Certainly it is decorative, for it has a soft orchid color, with a rim of white.
Drink is made of:
100% dry gin
10 dashes grenadine
White of an egg
1 sprig of mint
Fill glass with cracked ice, shake well, strain in champagne glass and serve.

Jacob Abraham Grohusko, Jack's Manual, 1910

CLOVER CLUB COCKTAIL.
The Juice of ½ Lemon or of 1 Lime.
1/3 Grenadine.
The White of 1 Egg.
2/3 Dry Gin.
Shake well and strain into medium size glass.

CLOVER LEAF COCKTAIL.
The same as CLOVER CLUB, with a sprig of fresh Mint on top.

Harry Craddock, 1930