1. Combine Ingredients for the Dough: In a large mixing bowl, gently whisk together the active sourdough starter and warm water until the starter is mostly dissolved. Add the bread flour and fine sea salt, then mix with a wooden spoon or your hands until a shaggy dough forms and no dry flour remains. Cover the bowl with a damp cloth or plastic wrap and let it rest for 30 minutes (this is called autolyse, which helps the flour absorb water).

2. Perform the First Set of Stretch and Folds: After the rest, uncover the dough. With damp hands, grab a portion of the dough from one side, stretch it upwards, and fold it over to the opposite side of the bowl. Rotate the bowl a quarter turn and repeat this stretch and fold motion three more times, completing one full round. The dough will start to feel more cohesive. Cover and let it rest for another 30 minutes.

3. Continue Stretch and Folds for Strength: Repeat the stretch and fold process (Step 2) three more times, with 30-minute rest periods in between each set. By the final set, the dough should feel noticeably stronger, smoother, and more elastic. It should be able to hold its shape better.

4. Bulk Fermentation (First Rise): After the final set of folds, cover the bowl and let the dough bulk ferment at room temperature (around 70-75 F / 21-24 C) for 3-5 hours. The dough should increase in volume by about 30-50% and appear bubbly. This is a crucial stage where the yeast and bacteria in the starter do their work.

5. Shape the Loaf: Gently turn the dough out onto a lightly floured surface. Avoid deflating it too much. Gently pre-shape it into a round ball by cupping your hands around it and pulling it towards you to create surface tension. Let it rest for 20 minutes. Then, shape it into a final round or oval (depending on your proofing basket/Dutch oven shape). For a round, gently pull the edges into the center, then flip it over and use your hands to create tension on the surface.

6. Cold Proofing (Second Rise): Carefully transfer the shaped dough, seam-side up, into a floured banneton (proofing basket) or a bowl lined with a floured kitchen towel. Cover it tightly with plastic wrap and refrigerate for 8-12 hours, or up to 24 hours. Cold proofing develops flavor and makes the dough easier to handle.

7. Preheat Oven and Dutch Oven: About 45-60 minutes before baking, place your Dutch oven with its lid into your oven and preheat to 475 F (245 C). It’s essential for the Dutch oven to be scorching hot.

8. Bake the Sourdough Loaf: Carefully remove the hot Dutch oven from the oven. Gently invert the cold dough from the banneton directly into the hot Dutch oven. Score the top of the dough with a sharp razor blade or knife (a simple cross or a single slash is common). Place the lid back on and bake for 30 minutes. Remove the lid, reduce the oven temperature to 450 F (230 C), and continue baking for another 15-20 minutes, or until the crust is deep golden brown and the internal temperature reaches 200-210 F (93-99 C).

9. Cool Completely: Transfer the baked loaf to a wire rack and let it cool completely for at least 1-2 hours before slicing. This allows the internal structure to set and prevents a gummy texture.