Add lime juice, sugar and eight mint leaves to a cocktail shaker.

Use the end of a wooden spoon or cocktail muddler to bash (or muddle) the mint into the lime juice and sugar. This releases oils from the mint and helps the sugar dissolve into the lime juice.

Add rum, stir well, and then pour into a glass filled with ice, leaving about an inch of room. Top with club soda and serve with extra mint leaves and a lime slice.