Wash the rhubarb and cut it into small pieces. Put in a saucepan, cover with the sugar and gently simmer for about 30 minutes until it is very soft and the bulk of the liquid has evaporated. The rhubarb should still be a vibrant colour. Remove the pan from the heat and allow to cool.
Puree the cooled rhubarb in a blender or food processor until fine, then put in a bowl and stir in the cream. Churn in an ice cream machine, then transfer to a tub and freeze. This may take about 4-6 hours.