Cut the peel of the peach crosswise and blanch for 1 minute in boiling water. Rinse in cold water and remove the peel. Cut the peaches in half and remove the pit. Cut into pieces. Soak with the raspberry liqueur. Puree the peaches with the powdered sugar. Stir in the sparkling wine.
Transfer into a metal bowl and freeze for 6-8 hours, stirring often with a fork to form a crumbly, ice crystals.
Pick the raspberries from the stem. Serve the peach granita in cold glasses garnished with raspberries and mint.