Place the raspberries (or blackberries), lime juice, mint and powdered Erythritol in 2 tall glasses.
You can keep a few berries for garnish.
Using a long spoon or a muddler, crush the berries and muddle the mint leaves to extract flavour.
Pour in white rum ...
...
add ice and top up with sparkling water (club soda).
Finally, garnish with more mint leaves, lime wedges and berries.
Enjoy!