Mix flour and water with the sourdough starter until all flour is incorporated. Let it ferment about 8 hours, or until the volume has increased considerably.

Mix flour and water and let it autolyze for an hour. Add salt, olive oil, and levain and mix until completely incorporated. Let the dough rest for 15 minutes and perform a stretch and fold. Repeat 2 or 3 times at 15 minutes interval.

Transfer the dough to a lightly oiled container. Let the dough ferment for 5 hours or until it has at least doubled in size.

Flour the working surface generously. Loosen the dough from the walls of the container with a plastic dough scraper by carefully inserting it between the dough and the walls. Turn the container upside down and let the dough fall down to the floured surface. Divided the dough into four pieces with a bench knife and pull them apart.

Flour a kitchen towel generously. Transfer the dough to the kitchen towel and stretch it to the desired size. Sprinkle flour on top of the dough and cover with another towel. Cover with cling film.

Proof for about 2 hours or until slightly over-proofed. Check with finger poke test.

Preheat the oven to 480°F/250°C. Cut 4 pieces of parchment paper to fit the size of the dough and place on a metal plate, a pizza peel, or a flat piece of wood, like a board. Place the plate with the parchment paper just beside one rectangle of dough and flip it over to the plate by dragging up the towel. Let the dough slide into the oven with the parchment paper.

Bake for 30 minutes. Let the ciabattas cool on wire rack.