For the yeast dough, heat milk and dissolve yeast in it. Mix flour, sugar and salt. Add yeast milk and fat and knead to a smooth dough. Cover and leave to rise in a warm place for 30 minutes. Knead dough again and roll out on a greased baking tray (42x36 cm).
Leave to rise for another 15 minutes. For the topping, drain the apricots well. Separate the eggs, beat the egg white until very stiff. Beat egg yolks, sugar and vanilla sugar until white-frothy. Stir in the sour cream, poppy seeds and lemon zest. Fold in the beaten egg whites. Press the yeast dough back to the edges of the baking tray after letting it rise, forming a small rim. Spread poppy seed mixture evenly on top. Spread apricot halves on top. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) in the lower third for 30-35 minutes.
Fold in the beaten egg whites. Press the yeast dough back to the edges of the baking tray after letting it rise, forming a small rim. Spread poppy seed mixture evenly on top. Spread apricot halves on top. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) in the lower third for 30-35 minutes. Let it cool down and dust with icing sugar. Results in approx. 20 pieces