Divide the sugar between 2 tall Collins glasses.
Squeeze 1 lime half into each glass
Add a mint sprig to each glass and muddle together with a long spoon.
Add a splash of soda to each glass and muddle further.
Divide the rum between the glasses, add 4-5 ice cubes to each glass and stir.
Add a dash of bitters to each glass.
Top with soda and garnish with mint leaves.