Clean, wash and cut the rhubarb into pieces. Mix starch with 2-3 tablespoons of red wine. Put the rest of the wine, liqueur, port wine, raspberry brandy, 125 g sugar and the cinnamon stick into a pot and bring to the boil. Add starch while stirring. Add the rhubarb and let it boil for 2-3 minutes. Pour into two gratin dishes (each 15 cm Ø; 1/4 litre capacity). Separate the egg.
Mix crème fraîche and egg yolk with the whisks of the hand mixer. Beat the egg white until stiff. Sprinkle in the remaining sugar and vanillin sugar. Add beaten egg whites to the egg yolk mixture and fold in carefully. Spread the gratinating mixture over the rhubarb and bake in a preheated oven (electric: 200 °C/ gas: level 3) for 8-10 minutes, if necessary switch on the grill. Serve the rhubarb au gratin sprinkled with pistachios