Preparation Stir first 3 ingredients in medium bowl until sugar dissolves. Blend peaches and reserved peach juices in processor until peaches are finely chopped. With machine running, gradually pour in sugar syrup; process until smooth. Add Prosecco and blend well. Transfer mixture to container. Cover and freeze until firm, at least 3 hours. (Can be made 2 days ahead. Keep frozen.)
Preparation Stir first 3 ingredients in medium bowl until sugar dissolves. Blend peaches and reserved peach juices in processor until peaches are finely chopped. With machine running, gradually pour in sugar syrup; process until smooth. Add Prosecco and blend well. Transfer mixture to container. Cover and freeze until firm, at least 3 hours. (Can be made 2 days ahead. Keep frozen.)