Bring the poppy seeds and milk to the boil and allow to swell over a low heat until a thick mash is formed. Stir in lemon zest and rum. Let the poppy seeds cool down. Stir the fat, sugar and vanilla sugar until creamy.
Stir in the eggs one by one. Mix flour and baking powder and gradually stir into the fat foam mixture. Finely dice the chocolate. Stir poppy seed mixture into 1/3 of the dough. Add the chocolate pieces to the rest of the dough.
Grease a ring cake tin (2 litres capacity) and sprinkle with breadcrumbs. Put the dough with the chocolate into the mould. Then add the poppy seed dough. Pull through with a fork (marble).
Bake in the preheated oven (electric: 175 ° C/ gas: level 2) for 60-70 minutes. Remove the cake and let it cool down a little. Turn out onto a cake rack and let it cool down. Serve dusted with icing sugar.
Results in about 16 pieces.