Combine the flour, yeast and salt in a large bowl and make a well. Dollop the yoghurt and oil into a measuring jug and add warm water to come up to the 350ml mark / to 1 cup plus 7 tablespoons. Give a quick beat with a fork to combine, then pour this liquid into the dry ingredients, and mix with your hands or a wooden spoon, adding more liquid as needed, to form a firm but soft dough.
Turn out onto a floured surface (or set your mixer and dough hook to work) and start kneading. Add more flour as needed until you’ve got a smooth, supple and elastic dough. Form the dough into a ball, grease a bowl and turn the dough in it so it’s lightly oiled all over. Cover the bowl with clingfilm and leave to rise for about an hour or so, until doubled in size.
Punch the dough down, then leave to rest for 10 minutes. Preheat the oven to 220ºC/gas mark 7/425ºF. Tear the dough into 3, and then halve each piece. Form each of these 6 little pieces into an egg-shape and, one by one, roll them out to make a flat, elongated, if irregular oval. Place on two baking sheets about 3cm / 1 inch apart, cover with tea towels and leave to prove for 20 minutes, until puffy.
Using the blunt side of an ordinary kitchen knife, draw diagonal parallel lines across the loaves about 2 cm / 1 inch apart. Do the same now the other direction, so you’ve got a loose criss-cross.
Beat the egg with the water and yoghurt and, using a pastry brush, paint this over the breads. Sprinkle on the nigella seeds and bake in the hot oven for 8-10 minutes, by which time the loaves will be golden, puffed up in places and cooked through.
Remove them from the oven and drape immediately and for a few minutes with a tea towel so that these small, flat, breads don’t dry up and get too crusty.