For syrup, combine the sugar, water and chopped mint in a large saucepan. Bring to a boil over medium heat; cook until sugar is dissolved, stirring occasionally. Remove from the heat; cool to room temperature.
Line a mesh strainer with a double layer of cheesecloth or a coffee filter. Strain syrup; discard mint. Cover and refrigerate syrup for at least 2 hours or until chilled.
For each serving, place ice in a metal julep cup or rocks glass. Pour 1/4 cup mint syrup and bourbon into the glass; stir until mixture is well chilled. Garnish with mint sprig.Yield: 10 servings (2-1/2 cups syrup).