Knead the flour, starch, baking powder, sugar, lemon zest, eggs, salt and butter into a smooth dough and chill the dough for 30 minutes.
For the filling, mix sugar, marzipan and rum into a spreadable mixture. This is best done in a suitable food processor, with a hand mixer it is a bit difficult. If the marzipan is spread on, you can also heat it up a little, then it is easier (15 seconds in the microwave). Crumble the sponge fingers and set aside.
For the crumble, use sugar, flour, butter and cinnamon to make fine crumble.
Roll out the dough on a floured work surface into 2 sheets of dough each (35 x 30 cm). Brush the pastry sheets with the marzipan mixture. Spread the raisins, biscuit crumbs and hazelnuts on top. Roll up the plates from the longer side and refrigerate for 1 hour.
Whisk the egg yolk and milk together and brush the rolling pin with it. Sprinkle with the crumble and cut into wide pieces. The recipe should make 16 pieces, I always prefer to make them a little bigger and then have 12.
Place the pieces of cake on a baking sheet lined with baking paper and bake in the preheated oven (electric stove: 200 ° C / gas: level 3) for 15 - 20 minutes. After 15 minutes at the latest, check that the sprinkles are not getting too dark. Afterwards, it should at most look golden brown, rather lighter. Otherwise it will be too dry.
Remove the bobbes, let them cool a little and dust with powdered sugar.