Combine all ingredients in a shaker without ice. Dry shake for 20 seconds, or until egg white is sufficiently incorporated. Add ice to the shaker and shake until chilled. Fine strain into a chilled coupe and garnish with Angostura Bitters on top.
The whiskey sour is a great cocktail, and adding an egg white to it makes it even better. The old school recipe typically called for an egg white, but it fell out of fashion and slowly turned into the whiskey and sour mix monstrosity that some bars serve.
You might hear this version of the whiskey sour referred to as a "Boston Sour" in some old cocktail books, but it's doubtful many people would know what you were referring to. There's a variation of this cocktail that adds a float of red wine to the cocktail called a New York Sour that I'll address in a later post.
Note: To make the heart pattern, drop 4 drops of Angostura bitters in the foam and drag a toothpick in a circular pattern through the dots.