Chop the chocolate coating. Heat the cream in a pot. Melt the couverture in it while stirring. Pour into a mixing bowl and cover and chill for at least 4 hours (preferably overnight).
For the compote, clean, wash and cut rhubarb into small pieces. 1⁄8 l Bring the rhubarb drink and sugar to the boil. Stir 1 tbsp. of it with starch until smooth. Stir back into the boiling juice, bring to the boil and simmer for about 1 minute while stirring.
Add rhubarb and simmer for 2-3 minutes. Pour compote into a bowl and let it cool down.
Finely grind the pistachios in the universal chopper. Whip the chocolate glaze cream with the whisks of the mixer for 4-5 minutes. Pour cream into a piping bag with a large perforated spout, squirt onto 8 butter wafers, add some compote and cover with 1 additional butter wafer each.
Dust with icing sugar and sprinkle with pistachios.