Make a syrup by simmering the sugar and water for 5 minutes. Leave to cool.
Wash the blackberries and rub them through a sieve into a plastic container.
Add the syrup and rosewater to the blackberry purée.
Place in the ice cream machine or deep freeze. If using the deep freeze bring out after an hour and stir. When semi-frozen pass in an electric whisker until smooth and fluffy. Freeze.