In a large glass, pour in the simple syrup and add the mint leaves. With the back of a spoon, muddle the mint leaves until they're broken and the mint oils have been released and you can smell them.

Pour in the bourbon and stir. Fill the glass with crushed ice. Garnish with a fresh mint sprig.

If you don't have any simple syrup, here is a simple recipe: In a small saucepan over medium heat, bring 3/4 cup sugar and 3/4 cup of filtered water to a boil. Then reduce the heat to medium low and stir constantly until the sugar is dissolved. This will take 3-4 minutes. Set aside. Store unused syrup in the fridge for up to two weeks.