Place the sugar and water in a medium saucepan. Bring to a boil over medium high heat, stir until sugar is completely dissolved. Remove pot from stove and allow syrup to cool, approximately 1 hour or longer.
Pour the bourbon into a small measuring cup. Add the mint leaves to the bourbon and let sit for at least one hour.
Combine the mint infused bourbon with the simple syrup.
Fill glass with crushed ice. Pour the bourbon and syrup combination over the ice and garnish with extra mint, if desired.