Heat 125 ml milk. Crumble yeast into the lukewarm milk and dissolve in it. Put the flour into a mixing bowl. Press a depression in the middle and pour in the yeast milk. Mix with some flour from the rim.
Sprinkle 120 g sugar and 1 sachet of vanillin sugar on the flour edge. Cover the bowl and leave to rise in a warm place for about 15 minutes. Meanwhile melt the fat, let it cool down a little. Knead the predough, liquid fat, 1 pinch of salt and egg with the dough hooks of the hand mixer to a smooth dough.
Let it go again for about 30 minutes. In the meantime, clean, wash and cut the rhubarb into pieces. Boil 220 ml milk. Mix 1/2 pack of custard powder, 3 tablespoons of milk and 20 g of sugar, stir into the boiling milk and boil for 1 minute while stirring.
Cover with cling film and allow to cool. Mix 2 tablespoons of cherry nectar, 1 packet of vanilla sugar and the rest of the pudding powder. Bring rhubarb and remaining cherry nectar to the boil. Stir in pudding powder and cook for 1 minute.
Knead the yeast dough again well and divide into 15 pieces. Roll out each piece to a square (10 x 10 cm) on a well floured work surface and beat all four corners inwards (like an envelope).
Place one tablespoon of custard in the middle of each and place it on 2 baking trays lined with baking paper. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 15 minutes.
Remove the yeast particles from the oven and brush with sugar syrup. Put a teaspoon of rhubarb compote on each particle and dust with icing sugar.