In a medium bowl, whisk together the flour, water, and yeast. Cover it with a towel and let rest until it’s bubbly all over, 3 to 3½ hours.

In the large bowl, combine the warm water, all of the sponge (from step 1), olive oil, flour, instant yeast, and salt. Mix vigorously with a silicone spatula until a shaggy dough forms and all the flour is absorbed. Cover and let rest for 30 minutes.

Wet your hands with warm water. With the dough bowl directly in front of you, slide your fingers or a wet bench scraper under one edge of the dough down to the bottom of the bowl. Pull that section of dough up, stretch it over to the opposite side of the bowl. Turn the bowl a quarter turn, and repeat 7 more times until you’ve made 8 folds and turns. (Continue to moisten your hands or the bench scraper so that the dough doesn’t stick.) Cover and set aside for 30 minutes.

Complete two more sets of 8 folds and turns (for a total of 3 times), resting for 30 minutes between each. After the last set, transfer the dough to a lightly oiled bowl. Cover and refrigerate the dough for 8 to 24 hours.

Remove the dough from the refrigerator and let sit at room temperature for 1 hour to warm up.

Sprinkle a work surface generously with flour. With a floured bench scraper, gently scrape the dough from the bowl onto the flour, being careful not to disturb any of the bubbles. Gently stretch it into a rectangle about 6 inches wide by 12 inches long. Starting at one of the short sides, fold one half of the dough over top of the other half, like you are closing a book. Pinch gently to seal the seams.

Stretch and press the dough into a 6 inch wide, by 10 inch long rectangle. Sprinkle the top generously with flour.

Using a bench scraper or very sharp knife, cut the dough in half lengthwise, pushing the two pieces away from each other as you cut, to create two long loaves.

Cut a large sheet of parchment paper in half lengthwise (to have 2 rectangles, about 6 inches by 16 inches each.) Carefully transfer the loaves to each sheet of parchment paper. Ensure the loaves are generously floured on top, then cover with a lint-free kitchen towel. Let rise for about 2 to 2½ hours, until the loaves are puffed and bubbles appear all over the surface.

After 1 hour and 30 minutes of rising, place one oven rack in the center of the oven and another oven rack in the lowest part of the oven. Place an overturned baking sheet or a baking stone or steel on the middle rack. Place a 10-inch oven-proof, heavy-bottomed skillet on the lowest rack. Preheat the oven to 475°F for at least 30 minutes before baking.

Once the loaves have finished rising, transfer the parchment paper with the loaves on it to the preheating baking sheet, stone, or steel in the oven. (A pizza peel or cookie sheet without a rim can help to transfer it easily.) Pull out the rack with the skillet and fill it with about 1 cup of ice cubes. Quickly push the oven rack in, then close the door. (This step is optional, but will help to create steam in the oven and make a crusty exterior).

Bake for 13 to 15 minutes, or until the ciabatta is deep brown and the internal temperature reaches 200°F. Transfer to a cooling rack to cool until warm. Slice with a serrated knife to cut through the crust.