On the evening of day one, mix together 1 Tablespoon active sourdough starter with 1/3 cup room temperature water. Stir to combine, then mix in 1/2 cup flour.
Cover and let sit at room temperature overnight.
On the morning of day two, dissolve 1 Tablespoon sea salt into 1/4 cup filtered water. Set aside.
Test your leaven by dropping a teaspoonful into a medium sized bowl filled with 2 1/4 cups filtered water. If your leaven floats, you're ready to proceed to the next step. (If your leaven sinks, feed your starter 2-3 times at 12 hours intervals until your starter doubles in size 2-4 hours after feeding.)
Add leaven to bowl of water and stir to combine.
Add flour, stirring in one cup at a time, until all flour is incorporated and no dry flour remains.
Cover bowl and allow to rest (autolyse) for 30 minutes (or up to 4 hours).
Give salt water a final stir to be sure all salt is dissolved. Using your hands, mix salt water into your dough. Stretching and folding until all water is incorporated.
Set a timer for 30 minutes. When timer goes off, stretch and fold the dough four times. Stretching from 12 o'clock down to 6 o'clock. 3 o'clock over to 9 o'clock, 6 o'clock up to 12 o'clock and finally 9 o'clock over to 3 o'clock.
Cover the dough and let rest another 30 minutes.
Continue steps 9 & 10 for 2 1/2 hours, or a total of 5 stretch and fold sessions.
Let your dough rest, covered, while you prepare your bannetons or towel-lined bowls.
Dust your banneton liners or towels generously with rice flour and set aside.
Carefully pour out your dough onto a well floured work surface.
Divide your dough into two equal portions.
Working with one dough at a time, take a pastry cutter, scoop up under your dough and shape into a loose ball with your hands (see photos).
Let dough rest for 15-20 minutes.
Again, working with one dough at a time, dust the top with a little flour and turn over so the top is now facing down.
Grab the dough at 12 o'clock and stretch and fold into the center of the dough. Work your way around the dough, stretching and folding at 3 o'clock, then 9 o'clock and finally 6 o'clock. Once you grab the dough at 6 o'clock, pull toward the center and grab 12 o'clock to flip the dough back over so the seam side is now down.
Lightly re-shape your dough to get a circle, if needed.
Transfer each ball of dough to a proofing basket, placing the top down and the seam-side up.
Wrap your baskets in plastic and let rise for 3-4 hours, or place in the refrigerator for 12-18 hours.
Once your dough has risen (whether on the counter or in the fridge) and you're ready to bake, place your Dutch ovens (or other baking options) in the oven and preheat to 500 degrees F.
Once preheated, carefully remove your pots, one at a time, from the oven and carefully dump your dough into the Dutch oven, seam side down. (Place dough straight from the refrigerator into the hot Dutch oven, no need to bring it up to room temperature first.)
Take your dough lame, or a sharp knife, and quickly score your dough, keeping at 45 degree angle, if possible (don't burn yourself in order to achieve this angle!).
Put the lid on the pot and place into the oven, repeat with other loaf and bake at 500 degrees for 20 minutes.
Reduce the oven temp to 450 degrees F and bake for another 10 minutes.
Remove the lids off your Dutch ovens (or pots) and continue baking for an additional 15-25 minutes until crust is golden brown, or to your preference.
Lift bread out of pots using a spatula and allow to cool completely on a cooling rack.
Once bread is completely cooled off, slice that baby open and enjoy your reward!