Liquidize the lemon juice and granulated sugar together until fine.
Mix the yoghurt with the double cream. Stir the sugared lemon juice into the yoghurt and churn in the ice-cream machine.
As with most ice-creams, this will take 15–20 minutes to churn, which still keeps it creamy before finishing in the freezer.
If you do not have an ice-cream machine, freeze until almos