In a glass, gently muddle the mint leaves and sugar to release the mint's essential oils. Be careful not to tear the mint leaves too much.
Pour in the fresh lime juice and white rum. Give it a good stir to mix the ingredients.
Fill the glass with ice cubes to chill the mixture.
Add soda water to fill the glass. Stir gently to combine.
Garnish with a mint sprig and a lime slice for an extra touch of elegance.