Clean, wash and slice the rhubarb. Bring rhubarb, 150 ml cherry nectar, sugar and cinnamon stick to the boil briefly in a pot. Stir pudding powder and remaining juice until smooth. Stir into the boiling liquid and bring to the boil again briefly.
Remove the cinnamon stick and let the compote cool down. Mix yeast and 1-2 tablespoons sugar. Put flour, remaining sugar, lemon peel and egg into a mixing bowl. Melt butter, add cold milk and pour the lukewarm mixture into the flour.
Add yeast and knead everything with the dough hooks of the hand mixer to a smooth yeast dough. Cover and leave to rise in a warm place for 30-40 minutes. Grease a fat pan (approx. 35x38 cm).
Knead the yeast dough again briefly. Roll out a good half of the dough on the fat pan. Spread the compote on top. Roll out the rest of the dough to the size of a baking tray on a floured work surface. Place on the rhubarb layer.
Press "dents" into the dough with two fingers and sprinkle with almond flakes, remaining sugar (40-50 g) and vanillin sugar. Spread the remaining butter in flakes on the dough.
Let the cake rise for another 15 minutes. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for 30-40 minutes. Remove the cake and let it cool down. Cut into about 24 pieces.
Serve with whipped cream as desired.