Heat 1/2 cup sugar and 1/2 cup water to boil. Boil 5 minutes; cool. Place 2 cups fresh mint leaves in 1 quart container. Pour sugar/water mixture over mint leaves. Cover tightly and refrigerate at least 12 hours but no longer than 24 hours. For each Mint Julep fill a 12 ounce glass with crushed ice. Add 1 1/2 teaspoon mint mixture with 2 ounce bourbon. Stir with long handled spoon until frost forms on outside of glass. Serve with a long straw and a sprig of fresh mint.