STEP 1: Mix starter and water. Whisk the bubbly starter and warm water together in a large bowl with a fork or spatula.
STEP 2: Add flour and salt. Mix in the bread flour and fine sea salt until well combined, finishing by hand if needed to form a rough dough.
STEP 3: Rest the dough. Cover with a damp towel and let rest for 30 minutes to allow the flour to fully hydrate.
STEP 4: Practice stretching and folding. After 30 minutes, grab a corner of the dough and pull it up and into the center. Repeat this folding technique 4 to 5 times.
STEP 5: Rest again. Let the dough rest for another 30 minutes before repeating the stretching and folding action. If time allows, perform this twice more for a total of 4 stretches and folds over 2 hours.
STEP 6: Finalize bulk fermentation. Cover the bowl and let the dough rise at room temperature for about 8 to 10 hours until it has increased by 50% in volume and has a few bubbles on the surface.
STEP 7: Shape the dough. Transfer the dough gently to a lightly floured surface and shape it into a round by folding the top down to the center.
STEP 8: Rest seam side up. Let the dough rest, seam side up, for 30 minutes.
STEP 9: Prepare for proofing. Line an 8-inch bowl or proofing basket with a towel and dust with flour.
STEP 10: Reshape and place in proofing basket. Shape the dough again and place it into the lined bowl, seam side up.
STEP 11: Refrigerate to proof. Cover the dough and refrigerate for 1 hour to 48 hours for an extended proof, ideally 24 hours for best flavor.
STEP 12: Preheat the oven. Place a Dutch oven in your oven and preheat to 550°F (290°C).
STEP 13: Prepare parchment. Cut a piece of parchment to fit your baking pot.
STEP 14: Invert the dough. Place the parchment over the dough and carefully invert the bowl to release the shaped dough.
STEP 15: Score the dough. Using the tip of a small knife or razor blade, score the dough's surface as desired.
STEP 16: Transfer to Dutch oven. Use the parchment to carefully transfer the dough into the preheated pot.
STEP 17: Bake covered. Lower the oven temperature to 450°F (230°C), cover the pot, and bake for 30 minutes.
STEP 18: Bake uncovered. Remove the lid, lower the oven temperature to 400°F (200°C), and continue baking for another 10 to 15 minutes.
STEP 19: Cool the loaf. If necessary, lift the loaf out of the pot and bake directly on the oven rack for an additional 5 to 10 minutes. Cool on a wire rack for 1 hour before slicing.