For this recipe, mash 1/4 cup blueberries. In your shaker, combine 6 mint leaves, the juice of 1 lemon and 1 tablespoon brown sugar. Crush gently using a muddler. Add the mashed blueberries and shake. Pour into a glass, and add 1 1/3 ounces of rum, sparkling water and ice cubes. Garnish with a lemon slice and a few fresh blueberries.