Place the juice, sugar, cornstarch and spices in a small pot and whisk until completely smooth. Mix in the rhubarb.
Bring to a simmer, and then very gently simmer until the rhubarb is just tender, but still holding its shape, about
5 minutes. (The mixture should be fairly thick.) Transfer
to a bowl, cool to temperature, and then refrigerate until well chilled. (Can be made several hours before needed.)
When ready to serve, whip the cream until soft peaks form. Add the icing sugar and beat until stiff peaks form.
Very delicately fold all but 1/3 cup of the rhubarb mixture into the whipped cream. Divide mixture between 6, 6 oz. decorative glasses. Top each glass with a spoonful of the rhubarb mixture. Garnish each glass with a mint sprig
Note: The rhubarb should be cut into ¼"–½" thick pieces. If you using frozen, drain it well after thawing.