On the evening before the baking day, mix the sourdough starter (saved from the last baking) with 200 ml of lukewarm water and 200 g of the rye flour. Cover and let rise overnight in a warm place for at least 12 hours.
Then knead the remaining ingredients into a soft dough. Be careful when adding water, first add 250 ml lukewarm water, then if necessary add more until the dough consistency is a little softer than with yeast pastries. Since the dough is a bit sticky, it is best to knead with the food processor for 5-10 minutes. Let the dough rest for 30 minutes, knead again vigorously and cover in a proofing basket and let rise for approx. 2 hours (if you do not have a proofing basket, a normal bread basket or a bowl covered with a floured kitchen towel will do).
In the meantime, heat the oven to 250 ° C before inserting the bread. Pour approx. 250 ml of boiling water into the hot oven (be careful not to scald with the steam). Put the bread on the hot baking sheet (even better pizza brick), turn the heat down to 200 ° C and bake for about 1-1.5 hours. The bread is ready when it sounds hollow when you tap the underside.