In a cocktail shaker or a tall sturdy glass, add 20 mint leaves and 2 lime pieces. Using a muddler, crush the mint leaves and lime pieces until the juice is released from the limes.
Add 4 more lime pieces and the sugar to the shaker. Muddle again to crush the limes and dissolve the sugar in the lime juice.
Spoon equal amounts of the lime and mint mixture into 2 highball glasses.
Fill the glasses almost to the top with ice. Pour the sparkling water over the ice to fill the glasses.
Garnish each glass with a mint leaf and a lime wedge. Enjoy.