Combine nectarine slices, raspberries and sugar in a small bowl and mash with a fork.
Add scoops of ice cream to 4 large glasses and divide most of the nectarine and raspberry puree among the glasses. Top each with a few more scoops of ice cream then the remaining puree. Fill the glasses to the top with the prosecco and drizzle each with some of the Chambord. Garnish with mint sprigs.