Make the Poolish (Day Before)
In a medium bowl, mix water, bread flour, and yeast until combined.
Cover loosely with plastic wrap and let sit at room temperature 12–16 hours, until bubbly and doubled in size.
Make the Dough
In a large mixing bowl, combine all of the poolish, bread flour, water, salt, and yeast.
Mix with a spatula until no dry flour remains — the dough will be sticky.
Cover and let rest for 30 minutes.
Stretch and Fold
With wet hands, grab one side of the dough, stretch it up, and fold it over itself.
Rotate the bowl 90° and repeat until all four sides are folded.
Repeat this stretch and fold process every 30 minutes for 2 hours (4 rounds total).
First Rise
Cover the dough and let rise for 1–2 hours, or until doubled in size and bubbly.
Shape the Ciabatta
Generously flour a work surface and gently turn the dough out (do not punch down).
Using floured hands, shape into a rough rectangle.
Cut into 2 equal pieces and gently stretch each into a longer slipper shape.
Place on a floured baking sheet or parchment-lined tray.
Final Proof
Cover loosely with a kitchen towel and let rest for 45–60 minutes.
Bake
Preheat oven to 450°F (230°C) with a baking stone or inverted baking sheet inside.
Place a shallow pan of hot water on the oven’s bottom rack for steam.
Slide the ciabatta onto the hot stone/sheet and bake for 20–25 minutes, until golden brown.
Cool on a wire rack before slicing.