Well, a happy World Pisco Sour Day to you!
Wait...what is a pisco sour? And what does it have to do with cookies? Read on.
To understand the pisco sour, first you must understand what pisco, a beverage hailing from Peru and Chile is, exactly. Pisco is a type of alcohol made with grapes, but it is not wine. It's distilled into a high-proof brandy. It's said to have been developed in the 16th century by enterprising Spanish settlers who wanted an alternative to spirits which they had to import from Spain. Pisco could be made with local fruit and didn't come with a hefty price tag or lengthy import time, so it's not too hard to see how it became an official Thing in no time at all.
So, pisco is a sort of bracing, acidic, but oddly not unpleasant, beverage. But to make it more palatable, it's softened with a "sour" mix to make the cocktail, which is basically a mix of citrus and sugar. Some versions have egg white, but not all.
If you're interested in making a pisco sour, this informative post offers info on ingredients and the method. Personally, I find the pisco sour an interesting cocktail, but it's never going to be my go-to drink. If you ask me, I'd rather eat a cookie made with pisco than drink a pisco sour.
As for the cookies? A couple of years ago I made pisco-infused alfajores, and they tasted splendid. They didn't include the sour mix, but how many cookies do you know of that have pisco in them? Maybe today is the day you give them a try?