01 - Combine bread flour, whole wheat flour, and water in a large bowl. Mix until just incorporated. Cover the bowl and let rest for 1 hour to allow gluten development.
02 - Add the active sourdough starter and sea salt to the autolysed dough. Mix thoroughly by hand or using a spatula until fully integrated and no dry flour remains.
03 - Cover the dough and let ferment at room temperature for 4-5 hours. Perform stretch and folds every 30-45 minutes by grabbing one edge of the dough and pulling it upward, then folding it over the center. Repeat this process 4 times total to build dough strength.
04 - Turn the dough onto a lightly floured work surface. Gently shape it into a round boule, using your bench scraper to help if needed. Cover and let rest for 20 minutes to relax the gluten.
05 - Shape the dough into a tight round loaf, creating surface tension. Place the loaf seam-side up in a well-floured proofing basket or lined bowl.
06 - Cover the basket and let rise at room temperature for 2-3 hours until increased by about 75%. For enhanced sour flavor, refrigerate overnight for a cold proof.
07 - Position a Dutch oven or heavy oven-safe pot with its lid on the center rack. Preheat oven to 480°F for at least 30 minutes to ensure thorough heating.
08 - Gently invert the dough onto parchment paper. Score the surface with a sharp blade or lame in your desired pattern. Transfer to the preheated pot, cover with lid, and bake for 20 minutes. Remove lid, reduce temperature to 430°F, and continue baking for 25 minutes until deep golden brown.
09 - Remove the bread from the Dutch oven. Transfer to a wire rack and let cool completely for at least 1-2 hours before slicing to allow the crumb structure to set properly.