In a saucepan over medium heat, cook rhubarb and sugar until rhubarb is soft and sugar is completely dissolved. This should take about 10-12 minutes. Remove from heat and let it cool.

Then, with a blender, food processor or stick blender, puree rhubarb until smooth. Place in refrigerator to get cold for about 15 minutes.

In a mixing bowl, beat cream until stiff peaks form.

Stir lemon into rhubarb puree, then, fold into the whipped cream. Place in freezer safe bowl and cover.

Place in freezer until sets. At least 4-6 hours before serving.