This is a century-old cocktail from Peru, where Pisco is the local aguardiente, an unaged grape spirit. It is basically a sour with an egg white, but that egg white makes all the difference.
This is not like any other classic cocktail. If you cannot sample it at any local restaurant or bar, then it is worth investing in a bottle of Pisco to sample it. There's a good chance that it will enter your repertoire of go-to cocktails!