Prepare a sourdough from the first three ingredients the evening before the baking day. Cover and leave to stand overnight at room temperature.
Add the remaining ingredients on the baking day and knead for 10 minutes. Let the dough rest for half an hour. Then fill the dough into 2 smaller proofing baskets or 3 mini-box molds (20x10cm) and let rise for another 30 to 60 minutes. If desired, brush with a little oil and cut or pinch it.