1.Cut peaches into quarters and remove the stones.
2.Combine sugar, vanilla and water in a medium saucepan. Stir over medium heat until sugar has dissolved. Bring to the boil, then reduce to a simmer.
3.Add peach quarters and cover. Simmer over a low heat, 5 minutes, or until tender. With a slotted spoon, remove the peaches to a bowl. Simmer syrup, a further 5 minutes, or until reduced to 1 cup (250ml).
4.Remove skin from peaches and pour over 4tbsp of syrup, reserve remaining syrup. Cover both reserved syrup and peaches with plastic wrap. Refrigerate until cold.
5.Just before serving, divide peaches among four serving plates. Combine frozen raspberries in a blender with chilled syrup. Blend to a smooth sorbet consistency, then immediately spoon over the peaches to serve.