Add all the ingredients, except for the bitters, to a shaker and shake vigoriously, without ice, for 10 seconds. This is called a dry shake—you'll fully emulsify the egg white this way.
Add ice and then shake vigorously again for 10 seconds, straining into a chilled cocktail glass. Top with a few dashes bitters or don't—it's creamy and flavorful all on its own.
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