The famous Prosecco cocktail appears here as a blackberry variation, fortified by a touch of Italian red vermouth.
Gently stir together blackberries, vermouth, and sugar in a bowl. Let stand, stirring occasionally, until blackberries release juices and sugar dissolves, about 1 hour.
Spoon 2 tablespoons of the blackberry juice and 4 blackberries into each of 6 Champagne flutes. Top each with Prosecco.