In a blender, puree the fresh blackberries until smooth. If desired, strain the puree through a fine mesh sieve to remove the seeds.

In a large pitcher, combine the blackberry puree and orange juice. If you prefer a sweeter drink, stir in the sugar until dissolved.

To serve, fill each champagne flute halfway with the blackberry-orange mixture.

Top off each glass with chilled sparkling wine or champagne.

Garnish with fresh mint leaves if desired.