This is a fairly wet dough so although you can make it by hand it’s probably easier to use a stand mixer with a dough hook.
Put the flour, water, salt and sourdough into a bowl and mix on a low speed for a couple of minutes until all the ingredients are mixed together.
Increase the speed slightly and continue to mix the dough for about 5 minutes. You will notice that the dough strengthens and begins to cluster around the dough hook. At this point, allow the dough to rest, covered, for about 10 minutes.
Next, add the olive oil. On a low speed, drizzle the oil into the dough and allow the dough to absorb the oil. Increase the speed slightly and mix for a further two minutes.
At this point cover the dough an allow it to rise in a warm place for 2 hours.
Every 30 minutes give the dough a stretch and fold (a total of four times), re-cover and put back in its warm place to continue rising.
Put a good glug of extra virgin olive oil into a rectangular pan or dish. Place the dough gently into the pan. At this point, don’t be tempted to stretch the dough into the corners of the pan.
Allow the dough to rise, covered, for a further 4 hours. After the first 3o minutes uncover the dough and gently stretch the dough into the corners of the pan. If you wet your hands to do this, the dough won’t stick to them. Repeat this process after another 30 minutes.
Allow the dough to rise for the remainder of the four hours until well risen and bubbly.
Preheat the oven to 230C
When your dough is ready to bake, liberally drizzle the top with more olive oil and sprinkle over the olives and some sprigs of rosemary.
Wet your fingers and dimple the dough all over, a bit like playing the piano! Press the olives and sprigs of rosemary well into the dough so they don’t burn.
Sprinkle the top with flaked sea salt and bake for about 30 minutes until the top and bottom are a lovely golden brown.
Best eaten on the day of baking, or trying chargrilling the next day if you don’t manage to eat it all!
NB If you wish to prove the dough overnight, place the covered pan in the fridge half way through the four-hour rise. The next day take the dough out of the fridge and allow it to come up to room temperature to finish its rise. It should be well risen with lots of lovely bubbles. Continue from point 10 for baking.