Pour water into a mix bowl. Add sourdough starter, whisk to mix it. Add brown bread flour and whole wheat flour, whisk it to mix well. Cover for 30 minutes.

Remove the dough to work on the surface sprinkle a little bit flour and cover for 20 minutes before form the dough. Cover and chill in the fridge over night.

Preheat the oven at 260 degrees celsius, transfer the dough into the pot cover rid. Bake 230 degrees celsius for 20 minutes. Open the rid and bake for 25 minutes.