Combine the sugar and boiled water in a small metal bowl. Chill to 4°C (39°F).
Peel the peaches, halve and remove the stones, and juice the flesh using a centrifugal juicer (the most common type available at appliance stores) with the vitamin C powder placed in the juice-collection jug. Pass the juice through a fine sieve lined with two layers of muslin (cheesecloth).
Combine the peach juice with the lemon juice, sugar syrup and salt. Check the balance of flavours — it shouldn’t be too sweet. Pour into a small stainless-steel tray and place in the freezer. Stir with a fork every 30 minutes to break up the ice crystals until it is completely frozen and a fluffy texture. Store in an airtight container in the freezer until needed. (You could prepare this the day before you want to consume the dessert but it will never taste as good as on the day it is made — peaches have a fragrance that diminishes over time.)
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