For the chia seed bread, mix the two types of flour. Put half of the mixture in a bowl and make a well in the center. Pour the sourdough mixed with 500 ml of water into this well and mix with a little flour.
Cover and let it rest overnight at room temperature. Add the remaining water with salt and crumbled yeast. Knead together with the remaining flour and the chia seeds to form a smooth dough.
Now cover this dough again and let it rise for about 3 hours. Now knead the dough again and form it into a loaf. Place the bread on a floured baking sheet and let it rise for another 90 minutes.
Preheat the oven to 200 °C. Brush the bread with a little water and sprinkle the chia and sesame seeds on top. Bake the bread for about 80 minutes. Let the bread cool and cut it the next day.