Place the sugar and cold water into a saucepan and stir, over a low-medium heat until the sugar is dissolved.

Increase the heat to medium and, without further stirring, allow to come to a gentle boil.

Place the mint leaves in a heat proof bowl. Once the sugar mixture has boiled, carefully pour it over the mint leaves and allow to sit and steep for up to 30 minutes.

Cut the watermelon in half and use a spoon to scoop out the flesh. Put the flesh into a food processor or blender. (Note: you can keep the seeds in as they will be removed when the mixture is strained in the next step).

Blend the watermelon flesh for a minute or two until you have a smooth consistency. Strain the mixture through a fine sieve to remove any bits of seed.

For every cup of watermelon juice you have, stir in 1 tbsp of minted sugar syrup and 1 tsp lime juice. Adjust to suit your taste.

Pour the mixture into a shallow, freezer-proof container and freeze for 2 hours. 

Remove from the freezer and use a fork to give the mixture a good stir, scraping the sides to remove any ice crystals that have formed. Return to the freezer for 1 hour. 

Repeat this stirring and scraping process every hour, making sure to use your fork to break up any large chunks of ice that form until the granita is completely frozen. This will take 5-6 stirrings.

Once completely frozen, transfer the granita to a sealed container and store in the freezer until required.