Place 8 champagne glasses in freezer for 20 minutes.
Combine 6 oz. frozen mixed berries (thawed), 1/4 cup orange juice and 1 Tbsp. sugar in a blender; blend until mixture is pureed, about 20 seconds. Strain berry mixture and discard seeds.
Add 1 Tbsp. berry puree to each glass and pour in enough chilled sparkling wine to almost fill glass. Garnish with fresh mint. Serves 8.