For the plum-poppy seed dough, mix flour, dry yeast, powdered sugar, salt, egg yolks, vanilla sugar and lemon zest. Heat margarine and milk and add to flour mixture and work into a yeast dough.
Cover the dough and let it rise for 30 minutes. Roll out dough onto smaller baking sheet and spread with plum jam. Place the removed plums in a fan shape on top of the dough and sprinkle with poppy seeds.
For the crumble, crumble flour, powdered sugar, margarine and cinnamon and spread over the plums. Bake the plum-poppy seed crumble in the preheated oven for about 30 minutes at 190 degrees.