Instructions

First separate the egg, put the egg white into a Cocktail Shaker and stir until the proteins break and froth forms. Then add the lime juice, simple syrup and Torrontés (AWI Torrontes, of course).

Fill Cocktail Shaker with ice and shake until the mix gets cold. Strain into a red wine glass, leaving the foam at the top of the drink. Garnish with 2 splashes of bitter angostura on the foam and a small sprig of Rosemary.

Tips (adapted from The Spruce)

Very tart lime juice is essential. Many sour recipes call for lemon juice, possibly a translation error from the Spanish word limon.  Limones are actually small South American limes, similar to key limes (also known as "Peruvian lemons").

Remember that the skin of limes has a lot of essential oils that can be a tad too bitter and sour, so when squeezing your limes, be sure to keep the flesh side facing down and not running down the lime peel. Also, don't drop the lime in as garnish after it’s been squeezed into your drink as it will also tamper with the taste.  

Keep the simple syrup really simple. You can use any recipe for simple syrup you want, but the easiest option is to forgo the weird sweeteners, artificial sweeteners or expensive syrups and just do 1:1 ratio of sugar to water and mix. 

Don’t be afraid of using real egg whites. You can always use pasteurized liquid egg whites from a container, but the texture is not quite the same and can affect the look and taste of an authentic pisco sour.

Shake your cocktail shaker well so that when you pour it into an old-fashioned glass, you get a nice 1/2-inch layer of foam on top.