1. Put the mint leaves, lemon, and syrup in a chilled cocktail shaker. Gently crush with a muddler or the end of a wooden spoon until the lemon wedges have released their juice. Add the whiskey and fill the shaker with ice. Put the lid on the shaker and make sure you have a tight seal. Shake as hard as you can for 7 to 10 seconds and then strain into a small chilled rocks glass filled with fresh ice. Garnish with the mint sprig and serve.