muddle one of the mint springs with the limes, lime juice and simple syrup in the bottom of a jar glass. add the gin and the simple syrup and shake well. pour into a goblet over crushed ice and stir until the outside of the glass frosts. top with soda and garnish with rest of mint.
*at least my beloved friend tobi who introduced me to this drink can think of a gazillion reasons why to have a southside every day.