Mix 200 ml milk, pudding powder and 6 tablespoons of sugar. Bring 1.3 litres of milk to the boil, remove from the heat and add the pudding powder while stirring. Bring to the boil again briefly, pour into a bowl, cover with foil and allow to cool in a cold water bath.
In the meantime warm 150 ml of milk. Crumble yeast into it and dissolve it. Put 400 g flour, egg, 50 g sugar, 50 g butter, salt and yeast milk into a bowl and work through with the dough hooks of the hand mixer until the dough starts to bubble.
Cover and leave in a warm place for about 30 minutes. Meanwhile sieve 250 g flour into a bowl. Knead 125 g sugar, lemon zest, 1 pinch of salt, vanillin sugar and 175 g butter with the dough hooks of the hand mixer.
Then work into crumbles with your hands. Grease an oven pan (32 x 38 cm) and sprinkle with breadcrumbs. Knead the yeast dough briefly and roll out thinly in the fat pan. Press the dough up at the edge with your hands.
Stir the pudding and sour cream until smooth. Spread on the dough and smooth it down. Sprinkle with crumbles. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 35 minutes.
Take out and let it cool down. Cut into pieces and serve lightly dusted with icing sugar.