Combine the warm water, instant yeast, and sugar in a mixing bowl, then let the mixture rest for 5–10 minutes until the yeast becomes slightly foamy and activated.
Next, add the oil and salt, then gradually mix in the bread flour until all the flour is hydrated and a soft, sticky dough forms with no dry patches remaining.
Cover the bowl and allow the dough to rest for 30 minutes. Then perform one round of stretch and folds by folding all four sides of the dough toward the center. Rest for another 30 minutes and repeat this process two more times, completing a total of three rounds until the dough becomes smooth, elastic, and stronger.
Cover the dough tightly and refrigerate for 24, 48, or up to 72 hours. All of these fermentation times produce excellent results, with longer fermentation developing a richer flavor and a lighter, airier crumb. When ready to bake, remove the dough from the refrigerator and let it come to room temperature for 1½–2 hours before baking. If you prefer to skip the cold fermentation, let the dough rise at room temperature until doubled in size, about 1½–2 hours, then bake.
Gently transfer the dough onto a lightly floured surface, divide it into four equal portions, and carefully shape each piece into a rustic ciabatta loaf without pressing out the trapped air bubbles. Lightly dust the tops with flour.
Meanwhile, preheat the oven to 225°C with a pizza steel or baking stone inside if using. Place a small oven-safe dish on the bottom rack and carefully pour in about 100 ml hot water just before baking to create steam.
Carefully transfer the shaped loaves onto the hot baking surface or a baking tray, then bake for 20–25 minutes until the crust is deeply golden brown, the loaves sound hollow when tapped underneath, and the internal temperature reaches 96–98°C.
Finally, transfer the baked ciabatta to a wire rack and allow it to cool for 20–30 minutes before slicing to achieve the best texture and crumb.