Start this recipe two days ahead to make the ice-cream.
Note Cedro is the glacé fruit of the citron tree, available from Simon Johnson, David Jones and select delicatessens. Agar-agar is a setting agent derived from seaweed and is available from health-food shops. Peach purée is available from The Essential Ingredient. If it's unavailable, poach 4 large peaches covered in a light sugar syrup (330gm caster sugar and 6 cups water) over low heat until tender (10-12 minutes), drain, discard skin and stone, purée flesh, then pass through a sieve.