Pour water in a 3-quart bowl. Add salt & yeast. Mix using a wooden spoon.
Mix in the remaining dry ingredients without kneading. Use a wooden spoon. You may need to use wet hands to incorporate the last bit of flour.
Cover (not airtight) and allow to rest at room temperature till the dough rises & flattens on top, roughly 2 hours. Refrigerate the dough without closing the container air-tight.
On the baking day, dust the refrigerated dough with flour & cut a pound size piece. Using a rolling pin & your hands flatten the dough about 1/2 inch thick.
Spread olives and roll up the dough to seal them inside.
Again crimp the ends and tuck them inside to form an oval dough. Place the dough on a pizza peel or worktop liberally sprinkled with semolina. Cover with plastic wrap or overturned bowl and allow to rise for 90 minutes.
Prepare the cornstarch wash by mixing 1 tsp of water with cornflour and then adding the remaining water. Boil or microwave the mixture till it becomes glassy.
Preheat the oven to 230 °C. Paint the loaf with prepared cornstarch wash. Slash in any pattern of your choice about ½ inch deep.
Slide the dough onto the baking tray, quickly cover with another aluminium pan to facilitate steam generation. Bake for 25 minutes covered, remove the overturned pan & bake for another 15 minutes to brown well.