The signature cocktail of the Diamondback Lounge bar of the Lord Baltimore Hotel, Baltimore, Maryland, USA. The hotel opened in 1928 and is still open, but the lounge is long gone. The cocktail featured in Ted Saucier's 1951 book Bottoms Up.
Half-fill a mixing jug with ice.
Add all ingredients and stir until well-chilled.
Strain into a tumbler over fresh ice.
Garnish with a sprig of mint.