• 250 g (generous 1 cup) caster sugar
• 8-10 limes
• 12 fresh lime leaves, sliced

Put the sugar in a saucepan with the zest of one of the limes and the sliced lime leaves. Add 250 ml (1 cup) water and heat very gently until the sugar has dissolved. Simmer for 5 minutes or until slightly thickened and syrupy. Set aside to cool and infuse for at least an hour or overnight in the fridge - it should be pale lime green and very scented.

Squeeze the limes to get 250 ml (1 cup) juice and add this to the sugar syrup. Strain through a nylon sieve. Taste for tartness and sweetness, remembering that freezing will mute the flavour so it should be extra punchy now.

If you have an ice-cream machine, churn and freeze according to instructions. Alternatively, transfer the syrup to a shallow container and freeze for about an hour, until the edges are frozen. Tip into a food processor, whizz to a slush and return to the freezer. Repeat a couple more times until you have a smooth sorbet. Return to the freezer for at least another hour.