Put the sourdough, flour, salt, grain mix and bread spices in a bowl. Grate the potatoes or puree them with a little buttermilk with a magic wand and add them to the other ingredients. Knead a dough out of it. The consistency is a bit firmer than a spaetzle dough.
Let the dough rest in the bowl for 30 minutes, shape it and place in a well-floured proofing basket and let rest in a warm place until cooked. This takes about 2 hours.
Then place the bread on the preheated baking stone at 250 ° C and bake for 10 minutes, then turn the oven back to 180 ° C and bake for another 50 minutes. In between sprinkle with water, preferably with a flower sprayer.