The Hanky-Panky cocktail was the brainchild of a Ada Coleman. Her benefactor, Rupert D'Oyly Carte, a member of the D'Oyly Carte family that first produced Gilbert and Sullivan operas in London, and the family that built the Savoy Hotel. When Rupert became chairman of the Savoy in 1903, Ada was given a position at the hotel's American Bar, where she eventually became the head bartender and made cocktails for the likes of Mark Twain, the Prince of Wales, Prince Wilhelm of Sweden, and Sir Charles Hawtrey.
Charles Hawtrey was the man for whom "Coley", as Ada Coleman was affectionately called, created the Hanky-Panky cocktail. He was an Victorian and Edwardian actor who mentored Noel Coward.
Coley herself told the story behind the creation of the Hanky-Panky to England's The People newspaper in 1925:
"The late Charles Hawtrey ... was one of the best judges of cocktails that I knew. Some years ago, when he was overworking, he used to come into the bar and say, 'Coley, I am tired. Give me something with a bit of punch in it.' It was for him that I spent hours experimenting until I had invented a new cocktail. The next time he came in, I told him I had a new drink for him. He sipped it, and, draining the glass, he said, 'By Jove! That is the real hanky-panky!' And Hanky-Panky it has been called ever since."
The Hanky-Panky is a variation on the sweet martini, inasmuch as it calls for gin and sweet vermouth, but Coley's secret ingredient was Fernet Branca, a bitter Italian digestivo. By adding just a couple of dashes of this herbal elixir, she transformed the drink into a masterpiece.
Pour all the ingredients into a martini glass half full of ice cubes. Stir well to combine and chill. Strain into a chilled martini glass.