Chill 2 martini glasses in freezer. Add all but 10 blackberries into a cocktail shaker. Muddle the blackberries. Add ice, and shake vigorously.
Double strain cocktails into 2 martini glasses. A double strain is using a Hawthorne drink strainer over the lip of the cocktail shaker, while pouring thru a fine mesh strainer, to pull out all the pulp from fruit.
Garnish each cocktail with 5 blackberries thru a cocktail pick.