Start the day before with the poolish. Mix the flour, water and yeast in a container and let it ferment overnight at room temperature.
On the next day, make the main dough. Add the fermented poolish, flour, remaining yeast and half of the remaining water and start kneading. Once the flour has absorbed the water, add the remaining water, salt, olive oil and yogurt. Knead until the dough is smooth.
Turn the dough out onto a work surface, stretch and fold it, shape it into a ball and let it rest in an oiled bowl for 60 minutes.
Divide the dough into four 220g pieces, shape them into balls, place them on a baking sheet lined with parchment paper and let them rest for another 60 minutes.
Brush the dough pieces with the egg yolk-yogurt mixture, make indentations, sprinkle with black cumin seeds and sesame seeds and bake for about 12 minutes at 250°C (480°F) with top and bottom heat.
Let the breads cool under a kitchen towel to keep them soft.
