The whiskey sour is a mixed drink containing whiskey, lemon juice, sugar, and optionally, a dash of egg white or cocktails foamer. Spirit, citrus and sugar combined to form the classic sour, one of the oldest types of cocktails. With the egg white, it is sometimes called a Boston Sour. The oldest historical mention of a whiskey sour was published in the Wisconsin newspaper, Waukesha Plain Dealer, in 1870.
Add bourbon, lemon juice, simple syrup and egg white, if using, to a shaker and dry-shake without ice.
Add ice and shake again until well-chilled.
Strain into a coupe glass.
Garnish with 3 or 4 drops of Angostura bitters.