Using a mortar and pestle, mash up blackberries and half of the mint. Alternatively use a straw and mash up very well so mint flavour soaks into the blackberries.
In a large bowl or jug combine club soda, lime juice, and vodka.
Divide blackberry-lime mix between two cups and add several ice cubes.
Pour vodka mix on top, splitting the mixture between the two cups.
Add 1 tsp of honey to each cup and divide the other half of the mint into each.