Whiskey Sour

45 ml (1.5 oz) bourbon
25 ml (~0.75 oz) lemon juice
20 ml (~0.75 oz) simple syrup
20 ml (~0.75 oz) egg white (Optional)

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Notes

One of the oldest cocktails in print, first published in Jerry Thomas's 1862 The Bartender's Guide. The egg white variation is sometimes called a Boston Sour. The sour family (spirit, citrus, sugar) is one of the foundational templates in cocktail making and likely dates back to sailors mixing spirits with citrus to ward off scurvy in the 18th century.