If your sourdough starter is not active and bubbly, go ahead and give it a feed 4 hours or more (depending on your starter's timeline to peak). You can use your starter anytime after peak.
In a large bowl, mix together the flour and water. Give it a really good mix with a spoon or a spatula and let it autolyse for 1 hour covered with a damp towel.
3 1/3 cups bread flour (13% protein or higher), 1 1/2 cups water (filtered)
After 1 hour passed, add the salt and sourdough starter. Mix the dough really well with a spoon or spatula. Let it rest covered with a damp towel.
1/3 cup sourdough starter, 2 tsp salt (I used Celtic salt)
After another hour, perform a set of stretch and folds (with wet hands). Cover and let it rest.
1 hour later, perform another set of stretch and folds (with wet hands). Cover and let it rest.
Bulk fermentation is ready when your dough has almost doubled in size (80-90%), and is really bubbly. When you gently shake the bowl, the dough should jiggle and look puffy.
To properly ferment the dough, don't look at the clock but rather the state of your dough. Fermentation times vary dependent on the temperature in your kitchen, the strength of your starter, the temperature of the water, and the protein content of your flour. Mine took about 8 hrs (after autolyse) at 68℉ (20℃) on average. In the summer, my bulk fermentation time can take half that time.
Sprinkle the dough with some flour, focusing on the sides of the bowl. Flour your working surface heavily.
With a floured bench scraper gently dump the dough onto your working surface. You need to be really gentle with the dough as it can deflate easily.
Use your scraper to gently push the sides of the dough and shape it into a rectangle. Do this without touching the dough with your hands.
Sprinkle quite a bit of flour on top of the dough and gently slice the dough into 3 equal rectangles using your bench scraper.
Prepare a floured parchment paper sheet to put the shaped ciabattas on.
With both your hands floured well grab a ciabatta from underneath on both sides and transfer it onto the parchment paper. Gently reshape the ciabattas as the transfer slightly ruins the shape. Use gentle hands to do this.
Let the ciabattas rest for about 20 minutes.
Preheat your oven to 465℉ (240℃) with your pizza stone (or cast iron griddle) inside. Boil 2 cups of water to have on stand-by.
After about 20 minutes, transfer the parchment paper with the ciabattas on the preheated pizza stone (or cast iron griddle). Either use a pizza sleeve or a thin chopping board for the transfer.
Pour the boiling water in an oven safe dish on the bottom of your oven after your placed the ciabattas in. This will create a steamy environment which is ideal for a good oven spring and nice crust.
Close the oven door and let the ciabattas bake for about 25-30 minutes or until golden brown. The ciabattas should sound hallow when you gently tap and have slightly puffed up. The crust should be hard to the touch.
Let the ciabattas cool completely on a wire rack.
Once they have completely cooled, you can slice it through the middle lengthwise (or slice it like a loaf, if you prefer).
The outside should be crusty and crispy and the inside should have an open crumb (large equal holes, light and airy texture). Be aware that sourdough is slightly chewier than conventional yeasted bread.
Serve and enjoy!