The poppy seed filling can be prepared ahead and will last in a jar stored in the fridge for up to a week.
1. Grind the poppy seeds in a coffee grinder almost to a powder.
2. Put the milk, sugar, vanilla seeds and the pod, and orange zest in a pan and bring to the boil. Fish out the vanilla pod and discard.
3. Add the poppy seeds and raisins and turn the heat down so it just simmers. Stir every now and then and cook for about 15 minutes until almost all the liquid is absorbed and the poppy seeds thicken considerably.
4. Add the lemon juice, the brandy and the butter, stir in and cook for another 3-4 minutes until the mix reaches thick, spreading consistency. Leave to cool.
5. For the dough, mix all the ingredients for the starter in a large bowl. Cover with cling film and leave for an hour in a warm place. In the meantime grind the cardamom seeds in a pestle and mortar and mix with the other spices and the sugar.
6. Add all the spice mix save for 1 tsp to the starter dough together with the ingredients for the main dough apart from the butter. Add a pinch of salt, then mix with your hands or in a standing mixer with the dough hook attachment for about 2 minutes. Add half the butter, then knead in the bowl for a couple of minutes before adding the rest of the butter. Knead until all the butter is mixed in and the dough is beginning to look silky smooth, stops sticking to your hands or bounces off the sides of the standing mixer bowl. Cover the bowl with a clean sheet of cling film and set aside to rise for 1 hour, punching it once to degas halfway through the time.
7. Divide the dough in half. Pat each piece down to form a rough rectangle, then roll it tightly from the top towards you. Leave it to relax for 10 minutes.
8. Flatten each roll and roll it up again from the narrow side, leave for another 10 minutes – this will tighten the dough and limit the risk of the log unfurling or cracking when baking.
9. Roll out each piece of dough into a rectangle about 30x30cm – it should be quite thin. Using a palette knife spread the poppy seed filling thinly all over the surface and roll it up tightly. Make sure the seam is sealed very well and tucked underneath the log.
10. Place the Mohnstollen on a baking sheet lined with parchment, cover with a clean tea towel and leave to prove for about 40 minutes. while the oven preheats to 200°C/180°C fan/gas 6.
11. Bake the Mohnstollen for 15 minutes or until they start to brown, then reduce the heat to 150°C/ 130°C fan/gas 2 and bake for further 35-40 minutes. If the tops turn dark quickly, cover loosely with foil.
12. Melt the butter in a small saucepan over a low heat. Remove the Stollen from the oven and leave to cool for a few minutes, then coat them at least twice all over with butter using a pastry brush. Mix the icing sugar with the remaining spice mix and dust the logs generously.