Divide the raspberries, lime and sugar between two tall glasses and muddle by gently crushing with a muddler or the end of a bar spoon. The fruits should start to release their juices, which will mix with the sugar.

Put half the mint leaves in the palm of one of your hands, then clap the other hand on top of the leaves – this bruises them just enough to release their flavour. Drop the bruised mint leaves into one of the glasses, then repeat with the remaining mint, dropping it into the second glass.

Add a handful of ice to each glass, followed by the rum. Stir, then top up with sparkling water. Stir briefly until just combined, then serve.