In a large mixing bowl, combine the sourdough starter and lukewarm water. Stir to dissolve the starter completely.

Add the bread flour and sea salt to the bowl. Mix until a rough dough forms, ensuring there are no dry spots. If needed, add 1 tablespoon more of water at a time until the dough is no longer dry.

Perform a series of stretches and folds on the dough. With wet hands, grab one end of the dough, stretch it upwards, then fold it over onto itself. Turn the bowl 90 degrees and repeat the process three more times. Cover and let the dough rest for 30 minutes. Repeat this step three more times at 30-minute intervals.

After the last series of folds, cover the bowl and let the dough rise at room temperature until it has doubled in size, approximately 6 to 8 hours, depending on the room temperature.

Turn the dough out onto a lightly floured surface and shape into a tight ball. Place the dough seam-side up in a floured banneton or clean bowl lined with a floured towel. Cover and let it proof for an additional 1 to 2 hours, or until slightly puffy.

Preheat your oven to 450°F with a Dutch oven inside. Once hot, gently place the dough into the Dutch oven, score the top with a sharp blade, and cover with the lid. Bake for 20 minutes, then remove the lid and continue to bake for another 20-25 minutes or until the crust is golden brown.

Remove the bread from the Dutch oven and let it cool on a wire rack for at least an hour before slicing.