Combine water and sugar in a saucepan and heat until the sugar dissolves. Remove from heat, add in basil leaves and let steep for 15 minutes. Strain leaves into a sterilised glass jars and then leave to cool.
Place a sieve over a sterilised glass jar and pour the syrup through it. Leave to cool and then use.
Method 1 : Freeze the bowl of your ice cream maker overnight.Place the fresh strawberries, cooled basil syrup, lime juice and white rum to a food processor or blender and blitz until smooth. Taste to check that the balance of sweet and sour is okay. Pour the mixture into your chilled ice cream maker and churn until the cocktail reaches a slushy consistency according to your ice cream maker's instructions. Method 2 : Place the frozen strawberries, cooled basil syrup, lime juice and white rum in a blender, blitz. Taste to check that the balance of sweet and sour is okay and then serve.