In a cocktail shaker, combine the whiskey, lemon juice, simple syrup, and egg white (if using).

Without ice, shake the mixture vigorously for about 15-20 seconds to emulsify the egg white and create a frothy texture.

Add ice to the cocktail shaker and shake again for another 15-20 seconds to chill the drink

Strain the mixture into a rocks glass filled with fresh ice. Garnish with a lemon wheel and/or maraschino cherry.