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