Feel free to play around with garnishes like whipped cream, shaved chocolate, Andes mints or even a Thin Mint Girl Scout Cookie (not going to lie, I just salivated thinking about that).
Combine all ingredients in shaker pint. Shake until cold. Strain into chilled coupe or martini glass. Garnish however you'd like.
Combine all ingredients over ice. Stir and serve. Garnish your heart out.
P.S. I always like to suggest playing around with your ratios of bourbon to liqueurs until you find what you like. I, personally, preferred the cocktail with 1.5oz of bourbon, 1.5oz chocolate liqueur and 0.5oz crème de menthe; but, I like my cocktails more spirit forward. If you prefer your cocktails with a little less whiskey in your face flavor, however, I would suggest using the measurements provided in the ingredients section.