Place the water, yeast and 55g of the olive oil in a jug – note: the water needs to be lukewarm (around 37°C) – stir to mix then leave to stand for 2 minutes.
Lightly oil a bowl and spatula and set aside. If using a stand (food) mixer, pour in the yeast mixture and then add the flour and 0.5 tsp salt, then knead for 1 minute 30 seconds. If kneading by hand, knead for 10 minutes.
With the aid of the oiled spatula, transfer the dough to the prepared bowl, cover the bowl with lightly oiled cling film and refrigerate for a minimum of 2 hours or overnight.
Line a baking tray with baking paper and grease it with 2 tbsp of olive oil. Transfer the dough to the prepared baking tray. With oiled hands, form the dough into a round shape. Cover the dough with lightly oiled cling film and leave it to rise in a warm place until doubled in size (approx. 30 minutes).
Now make the yogurt sauce – mix all of the ingredients together in a small serving bowl and refrigerate until ready to serve.
Preheat the oven to 200°C.
Without kneading the dough any further, spread it out with oiled fingertips into a rectangle (26cm x 30cm) and set aside.
In a bowl, weigh in 30g of olive oil. Add the zaatar and remaining 0.75 tsp of salt to the olive oil and mix it together. Brush the flatbread with the zaatar and olive oil mixture and allow it to rise for further 15 minutes in a warm place.
Bake for 20 to 25 minutes or until golden brown. Serve warm, cut in squares with the yogurt sauce.