Mix the butter, eggs and sugar until foamy, add the yoghurt and poppy seeds. Mix flour with baking powder, cinnamon and lemon zest and fold into the mixture. Spread the mixture on a greased and floured tray. Bake on medium heat for about 35 minutes. Take the baked yoghurt poppy seed slices out of the tube and let them cool down. For the glaze, mix the lemon juice and icing sugar together well. Cover the cooled yoghurt poppy seed slices with the lemon glaze. Serve the yoghurt poppy seed slices with whipped cream and berries.