12 whole mint leaves plus extra to serve
Juice of one lime
100ml white rum
Ice, for shaking
A splash of soda water
Put the blackberries, water, sugar, mint and lime in a cocktail shaker and mash with the end of a rolling pin. Add the rum and some ice and shake well.
Put the extra mint leaves and some ice into a glass and sieve in the cocktail adding a splash of soda water. Garnish with lime wedges, mint and blackberries by scattering on the cocktail.