In a shaker, combine sugar, lime juice, 8 blackberries and 12 mint leaves. With a muddler or the back of a wooden spoon, crush the ingredients until mint leaves are minced and sugar is mostly dissolved. Add crushed ice to 2 low ball glasses. Divide the mixture between the glasses. Add 1 jigger of rum to each glass. Add club soda to fill to the top. Garnish with mint leaves, additional blackberries and lime wedges.
