For the whiskey julep cocktail, place the mint in a glass and press lightly with the muddler (pestle). Pour the bourbon whiskey and sugar syrup into a pre-chilled glass, let it steep for about 5 minutes, stirring repeatedly.
Remove the mint, fill the glass with crushed ice and stir until the outside of the glass fogs up. Fill up with crushed ice and decorate the whiskey julep cocktail with the remaining mint.