For the levain, combine all ingredients in a bowl and stir well until fully mixed and it forms a thick batter. Cover lightly and let rest at room temperature overnight.
15 grams active sourdough starter (2 tablespoons), 75 grams unbleached bread flour (¼ cup + 3 tablespoons), 75 grams water (⅓ cup)
In a small bowl, dissolve the salt in 50g (4 tbsp) of water, stirring occasionally.
Add the remaining water to the levain and stir with a spatula to dissolve the levain into the water. Add the flour and stir with the spatula to form the dough. Cover the bowl with a kitchen towel and let rest at room temperature for 45 minutes.
525 grams water (2¼ cups), 725 grams unbleached bread flour (5¾ cups), 1 Tablespoon sea salt
Add the salt water to the dough and mix it in by hand. The dough will still be very loose and wet.
Fold the dough. Starting on one side of the dough and moving clockwise, grab the dough and fold it over onto itself. Repeat 4 times. Let the dough rest for 30 minutes and then repeat the folding and resting process 6 more times.
With the folds complete, cover the dough with a kitchen towel and let rest at room temperature for one hour.
On a lightly floured work surface, turn the dough out and, using a bench scraper, cut the dough in half. Be sure to work gently so as to not deflate the dough too much.
Gently shape the dough halves into balls using the bench scraper and your hands. Cover loosely with a kitchen towel and let the dough rest for 30 minutes before the final shaping.
Place two clean kitchen towels in the bottom of two medium sized mixing bowls and dust heavily with flour, rubbing it in to make sure they are fully covered.
Dust the tops of the dough balls with flour and, using your bench scraper, turn the dough over so the floured surface is on the bottom and the un-floured surface is facing up. Working clockwise, repeat the folding method from Step 5, folding 4 times. On the last fold, flip the ball over so the floured surface is facing up.
Dust the dough generously with flour and place them into the towel-lined mixing bowls. Cover the bowls with plastic wrap and let them rest in the refrigerator overnight.
Place two Dutch ovens (with the lids on) into your oven and heat it to 500F. When heated, carefully remove the Dutch ovens and slide the dough into the pots, seam side down.
Using a lame (or very sharp knife or razor blade,) score the dough. Replace the lids and bake covered for 30 minutes.
Reduce the oven temperature to 425F and bake for another 10 minutes, covered.
Remove the lids and bake for 25-30 minutes, checking the progress to make sure the crust is beginning to form.
Continue to bake the bread for 15-25 more minutes or until the bread is deep golden brown and crispy.
Remove and let cool completely on a wire rack.