In the deliciously darkened corners of the Vesper cocktail bar, in the central quartier of the Siamese capital known as Silom, the patrons are guzzling some of the finest cocktails east of Suez: from the exquisite complexities of the “Silver Aviation” (Roku gin, Prosecco, maraschino, coffee-walnut bitters, almond and lavender cordial), all the way to the heady simplicity of the “Mango Manhattan” (bourbon, vermouth, white port, absinthe).