Boil sugar and water, stirring often, 2 to 3 minutes or until sugar dissolves. Remove from heat; add fresh mint sprigs, and cool completely. Cover and chill 24 hours. Strain syrup; discard solids.
Grapefruit-Honey Syrup: Prepare Mint Syrup as directed, reducing sugar to 1/2 cup and stirring 3/4 cup fresh grapefruit juice, 1/2 cup honey, 3 (2- x 4-inch) grapefruit rind strips, and rind from 1 lime, cut into strips, into sugar mixture with mint. For julep, muddle with 1 small grapefruit rind strip. Makes 2 2/3 cups.
Peach-Basil Syrup: Prepare Mint Syrup as directed, substituting basil for mint and stirring 2 (5.5-oz.) cans peach nectar and 1 split vanilla bean into sugar mixture with basil. For julep muddle with 1 peach slice. Makes 3 1/3 cups.
Blackberry Syrup: Prepare Mint Syrup as directed, adding 6 oz. fresh blackberries, halved, with mint. For julep, muddle with 2 fresh blackberries. Makes about 2 1/2 cups.
Pineapple-Lemongrass Syrup: Prepare Mint Syrup as directed, reducing granulated sugar to 1 cup, adding 1/2 cup light brown sugar to granulated sugar and water, and stirring 1 cup pineapple juice, 2 Tbsp. fresh lime juice, and 3 (3-inch) pieces fresh lemongrass into sugar mixture with mint after removing from heat. For julep, muddle with 1 small fresh pineapple chunk. Makes 2 2/3 cups.