01 - Fill a cocktail shaker with ice cubes to chill the vessel.
02 - Pour Irish whiskey, green crème de menthe, lemon juice, and simple syrup into the shaker.
03 - Shake vigorously for approximately 15 seconds until the mixture is thoroughly chilled.
04 - Strain the cocktail into a chilled cocktail glass.
05 - Garnish with a lemon twist or fresh mint sprig and serve immediately.