In a large mixing bowl, combine the flour and salt. Add this to the starter.
Add the warm water (25-35 degrees), and olive oil to the flour. Mix with a spatula until a dough forms.
Make sure there are no dry flour streaks. Combine everything well, (the dough will be a little sticky at this stage), cover it with a damp cloth or plastic wrap, and let it rise in a warm place for about 1 hour or until it has doubled in size.
Gently transfer them to a floured surface. (Don´t press and release the gas).
Shape them into a log and divide it into 2 equal halves.
Cupping your hands below, form a ball.
Transfer them to a baking tray lined with parchment paper.
Place the dough in the centre of the tray and start stretching with even thickness all around.
Repeat the same for the 2nd ball.
Cover the loaves with a damp cloth or an oiled plastic wrap and let them rise for another 25-30 minutes.
In a small bowl, mix the beaten egg yolk, yoghurt, and water.
Brush the tops with the egg mixture.
Using your fingers, gently press a border around the edges of the dough to create a rim.
Press the dough to create a pattern. Gently make indentations in the shape of a grid or concentric circles, without cutting all the way through.
Sprinkle with sesame seeds and nigella seeds if desired.
Preheat your oven to 240°C. Bake for about 12-15 minutes, or until the bread is golden brown and sounds hollow when tapped on the bottom.