Combine all the ingredients in a mixing bowl using a sturdy spatula. Don't use your hands. This is a very wet dough. Make sure there is no more visible dry flour. Cover and let it rest for 30 minutes
4 sets of stretch and folds every 30 minutes:
After the rest, lightly wet your fingers, scoop and grab the edge of the dough from the bottom and gently wiggle it up to stretch it as far as it allows you to (don't force it and tear the dough)
Then fold over to the center. Repeat this with the next edge. You can probably do about 4-5 stretches and folds for this first round.
Round it up into a dough ball with the smooth side up. Cover it back again and rest for another 30 minutes
Perform the second and third set of stretch and fold like you did before. Notice the dough gets stronger now and not as slack. It won't allow you to stretch as far as the first round. You can probably do about 4 stretches and folds each round.
To bake on the same day:
After the 4th set of stretch and fold, cover and let the dough proof until it doubles in size at a warm place, this may take 30 minutes to 1 hour or longer and then proceed to the shaping step after that
If not baking on the same day:
After the 4th set of stretch and fold, transfer to a lightly oiled container with a tight-fitting lid, to prevent sticking. Put this in the fridge to let it cold ferment for 12-16 hours and then proceed to the shaping step after that
Shaping:
Prepare a baker's couche or a large stiff linen that can help to support the ciabatta during proofing so the dough won't lose its shape
Generously flour the couche to prevent sticking
I also cut four pieces of parchment paper, about 6-7 inches square to put the ciabatta on top
Dust your work surface with flour. Dust the top of the proofed dough with some flour too.
Tip the bowl/container upside down to let the dough slowly release and plop down onto the work surface.
Sprinkle some flour around the edges of the dough
Gently stretch the dough out a bit to make it more squarish in shape
We will divide the dough into 4 equal sizes. I dust the dough along the axis, the place where I will cut the dough using a bench knife, to prevent sticking.
After cutting use a bench knife to help you shape the dough to make it more square in shape and again, use a bench knife to help you gently scoop the dough and place it on top of a parchment paper you cut earlier, top-side down.
Repeat this with the rest of the three doughs. Pleat the couche in between dough to support the sides as they proof so they won't spread out and lose its shape
Final proofing:
Let the dough proof again at a warm place until they are really puffy, about 45 minutes to one hour. This will take longer if your dough has been in the fridge before
Baking with steam:
UPDATE (read my short post below why I use this safer method): Put a baking stone or baking steel inside the oven's middle rack and a cast iron pan next to it (not on the baking stone/steel). Fill up the cast iron pan with about 2 cups of water (room temperature water is fine). Start preheating the oven with the baking stone and a cast iron pan filled with water inside the oven, to 500 F (260C) for conventional oven, 475 F (250 C) for convection oven for at least 30 minutes.
If your cast iron pan is too large, you can put in one rack below it, but more to the side, not directly underneath the baking stone/steel so the steam can easily reach the bread during baking
Carefully slide the proofed ciabatta onto a baking peel. Make sure to protect your arms with oven mittens. Open the oven door and carefully slide the dough onto the baking stone, two at a time. Work quickly, but don't rush and be careful! After all four doughs are in, quickly close the oven door to prevent the steam from escaping too much
Reduce temperature to 475 F (250 C) and bake with the steam for 15 minutes. For convection oven, reduce by 20 F (15 C). Then carefully remove the cast iron pan and reduce the temperature to 450 F (230 C) for conventional oven. Lower the temperature by 20 F (15 C) for convection oven and bake for another 5 minutes or until the bread is golden brown. The internal temperature should be at least 200 F (93 C)
Cool down:
Remove from the oven and transfer to a cooling rack to let them cool down completely before slicing