Put the sugar and clementine zest in a small pan and cover with 150ml (1?4pt) water. Bring to the boil, then simmer for 5 minutes until the sugar has dissolved and the mixture has turned syrupy. Remove from the heat and leave to cool. (If using freshly-pressed clementines, pass the fluid through a fine sieve.) Combine the clementine juice and lemon juice with the syrup and stir. Pour into an ice cream machine and churn following the manufacturer's instructions. Alternatively, pour into a freezersafe container, seal with a lid, chill for 1 hour, then whisk every 30 minutes for 2 hours to break up the ice crystals. Freeze until firm. Remove the sorbet from the freezer around 10 minutes before serving to soften a little. To serve, scoop into glasses using an ice cream scoop and garnish with mint, if you like. Freezing and defrosting guidelines In order to enjoy optimum flavour and quality, frozen items are best used within 3 months of their freezing date. Always defrost and heat thoroughly before eating. For more tips on freezing and defrosting food, read our article Love Your Freezer.