Combine the sugar, 1/2 cup water, vanilla bean and seeds in a small saucepan. Bring to a boil and cook until the sugar is melted. Remove the vanilla bean, transfer to a bowl, cover and refrigerate until cold, about 1 hour.
Combine the vanilla sugar syrup and chopped peaches in food processor and process until smooth. Put some of the puree into the bottom of 4 Champagne flutes, or a pitcher. Top with cold sparkling wine and garnish with sliced peaches and mint sprigs.