Cocktail of the week: Pistachio Sour, STK The poor old whisky sour is one of our most historic, but overlooked, cocktails. A simple mix of whisky, lemon juice, sugar and egg white, it makes an appearance in the very first cocktail book, Jerry Thomas's The Bon Vivant's Companion or How to Mix Drinks (1862) and is described by cocktail expert David Wondrich as "the fried-egg sandwich of American mixology." But in a world where the restaurant Hawksmoor has a "nuclear banana daquiri" on its menu, so plain a drink is not likely to attract many disciples. A gradual revival of interest in classic cocktails however means that you'll probably spy the drink on a few cocktail menus these days - especially in the form of jazzed-up, flavoured variations. At STK restaurant in London, bar manager Sam Cortez has created a pistachio sour which gives a pleasant nutty edge to the classic drink. The mix of sour, sweet and nuttiness creates, he says, "an explosion of flavors on your taste buds, but it's still a well-balanced cocktail." The whisky he uses is rye, though you could replace it with the more easily-available bourbon, and you can omit the egg white if you're squeamish about salmonella. The egg does serve to soften the sourness slightly however, and gives the drink a silky, frothy quality it will otherwise lack. 50ml rye whiskey (STK uses Pikesville)