Step 1: In a large bowl, combine the active sourdough starter and warm water. Mix gently until the starter is mostly dissolved.
Step 2: Add the flour to the wet ingredients. Mix with a spatula or your hands until no dry spots remain and a shaggy dough forms. Cover the bowl with a damp cloth or plastic wrap and let it rest for 30 minutes (autolyse).
Step 3: Sprinkle the salt over the dough. Gently fold the dough over itself a few times to incorporate the salt evenly.
Step 4: Over the next 2-3 hours, perform 3-4 sets of stretch and folds. Wet your hands, grab a portion of the dough from one side, stretch it up, and fold it over the center. Rotate the bowl and repeat until you've gone around the entire dough. Repeat this process every 30-45 minutes.
Step 5: After the stretch and folds, cover the bowl and let the dough bulk ferment at room temperature (70-75°F / 21-24°C) for 8-12 hours, or until it has noticeably increased in volume (at least 50% or doubled) and is bubbly.
Step 6: Gently turn the dough out onto a lightly floured surface. Pre-shape it into a loose ball by folding the edges towards the center. Let it rest for 20-30 minutes, covered.
Step 7: Lightly flour your hands and the dough. Gently stretch and fold the dough into a tight ball, building tension on the surface. Place it seam-side up into a floured banneton basket or a bowl lined with a floured kitchen towel.
Step 8: Cover the banneton and place it in the refrigerator for at least 4 hours, or preferably overnight (up to 24 hours).
Step 9: About an hour before baking, place your Dutch oven (with the lid on) in your oven and preheat to 475°F (245°C).
Step 10: Carefully remove the hot Dutch oven from the oven. Gently invert the cold dough into the Dutch oven. Using a sharp razor blade or lame, score the top of the dough. Cover and bake for 20 minutes.
Step 11: Remove the lid and continue baking for another 25-35 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210°F (93-99°C).
Step 12: Transfer the bread to a wire rack and let it cool completely for at least 1-2 hours before slicing to prevent a gummy texture.