In a rocks glass, add:

1/4 oz simple syrup
10 large mint leaves

With a muddler, gently massage combine the ingredients, lightly pressing to get the mint oils off of the leaves. Do not over pulverize. Next, add:

2 oz bourbon

Fill the glass with crushed ice (cubes will work) and gently stir until leaves are dispersed and the drink is mixed. Garnish with a mint sprig