Cut the rhubarb stalks into bite-size pieces.
Gently cut the vanilla bean lengthwise to release the full flavor.
Mix all the ingredients together except for the cream and chocolate.
Simmer over a medium heat for 15 minutes. The rhubarb should fall apart when done. Set to one side and allow to cool.
Bring half of the heavy cream to the boil. Pour the cream over the chopped chocolate and mix with a hand-held mixer. Blend in the rest of the cream and leave to cool.
Serve the cold rhubarb mixture in dessert bowls. Beat the chocolate cream mixture until it resembles whipped cream and place a large dollop on top of the rhubarb.