Mix both types of flour, make a large well and pour in the sourdough.
Mix well and, depending on the consistency, add water and season. Knead into a ball of dough and let rest for a few hours.
Knead vigorously and work into a loaf, leave to rise for about 2 hours. Place on a baking sheet lined with baking paper and put in the preheated oven at 250 °. Add a bowl of water, steam tightly for the first 1/4 hour,
then switch back to 190 ° and bake for another 50 minutes.