For the broom bread, mix the sourdough, flour and starter with 80 ml of warm water and leave to mature in a warm place, covered, for approx. 16 hours.
Mix well the pre-dough, flour and yeast with 30 ml of warm water and leave to mature covered in the refrigerator overnight. Mix the pregelatinized dough, breadcrumbs with 50 ml of warm water and let it swell, also covered, in a warm place overnight.
Knead the main dough, sourdough and the remaining dough ingredients well with 430 Ml cold water and then let rest for 3 hours.
Then work it round on a well-floured work surface and place it on a floured kitchen towel with the end facing up and wrap it in it. Let rest again for 1 hour.
Then bake in a preheated oven for 10 minutes at 280 °C, 40 minutes at 220 °C and 20 minutes at 200 °C.