Prepare sourdough starter the night before by mixing starter with water and flours and letting it sit until doubled in size.
Prepare poolish the night before by mixing dry yeast with water and flour and fermenting at room temperature.
Next morning, mix water, poolish, starter, and flours for the main dough. Let rest for 1 hour.
Add salt, mix, and incorporate extra water gradually. Add olive oil and mix well.
Oil a container, transfer the dough, and let it rest. Perform four stretch and folds at intervals.
Let the dough rise until it reaches 30-40% increase in volume.
Shape the dough, proof, and preheat the oven with a baking stone and tray with ice cubes.
Bake the ciabattas at 500F, then reduce temperature and continue baking until done. Let cool before slicing and serving.
