Chop the chocolate coating. Heat the cream in a pot. Add couverture and melt while stirring. Pour into a mixing bowl, cover and leave to cool for at least 4 hours (preferably overnight).
Meanwhile wash and clean the rhubarb and cut it into small pieces. Bring 125 ml juice and sugar to the boil. Stir starch and 1 tbsp. rhubarb juice until smooth. Stir into the boiling juice, bring to the boil and simmer for about 1 minute while stirring.
Add rhubarb, bring to the boil and simmer for 2-3 minutes. Remove from the heat and pour into a bowl. Place in a cool place for about 30 minutes.
Finely grind the pistachios in the universal chopper. Beat the chocolate glaze cream with the whisk of the hand mixer for 4-5 minutes until stiff. Pour cream into a piping bag with perforated spout, squirt onto 8 butter wafers, add some compote and cover each with another butter wafer.
Dust with icing sugar and ground pistachios.