Guillermo Toro-Lira is probably the US's leading pisco historian, devoting years' worth of study to drinks such as the Pisco Punch and Pisco Sour. The latter drink was created by Victor Morris, an American who moved to Peru with the mining trade and opened a bar. Toro-Lira got hold of the register of Morris' bar, and this revealed many truths about the history of the Pisco Sour.
For background, the Pisco Sour is a simple sour, made with pisco, lemon or lime, sugar, and often an egg white and bitters. It is no revelation, based on the traditional sour recipe, but in this case we have a good idea of its origin. Pisco is a grape brandy from Peru and traditionally distilled in pot stills and unaged, as opposed to Chilean pisco that is a latecomer, usually distilled in column stills and sometimes briefly aged.
To read Toro-Lira's recent discoveries and theories based on Morris' bar register, check out the article here.