In a bowl, mix together the flour, yeast, nigella seeds and salt. Add 120ml/4fl oz of the water and 1½ teaspoons of oil. Using your fingers mix the ingredients together. Gradually add the remaining water and oil until all the flour has come away from the sides and you have a soft dough. (You may not need all the water; the dough should be soft and not sticky.)
Pour a little oil onto your work top. Place the dough on top and knead for 5-10 minutes. The dough will be wet in the beginning but will form a smooth dough once kneaded. Once a smooth dough is achieved, place it into a clean, oiled bowl. Cover and leave to prove until doubled in size.
Preheat the oven to 250C/475F/Gas 9 and place a clean baking tray or baking stone on the middle shelf.
When the dough has doubled in size, tip it out onto a work surface dusted with flour. Knock the dough back by folding it inwards over and over again until all the air is knocked out. Split the dough into 4-6 equally sized balls. Roll each ball into an oval shape 3-5mm thick.
Remove the hot tray from the oven, dust with flour and place the pitta breads on it. You may have to cook them in batches.
Bake for 5-10 minutes, or until they just start to colour. Remove them from the oven and cover with a clean cloth until they are cool.
Pitta breads are best eaten the same day or frozen for later use.