01 - Combine bread flour, whole wheat flour, and water in a large mixing bowl. Stir until just incorporated and no dry flour remains. Cover the bowl and let rest for 1 hour at room temperature to hydrate the flour.
02 - Add the active sourdough starter and sea salt to the autolysed dough. Mix by hand using a squeezing and folding motion or use a spatula until fully incorporated. The dough should feel smooth and elastic.
03 - Cover the bowl and let the dough ferment at room temperature for 4 to 5 hours. Every 30 to 45 minutes, perform a stretch and fold: grab one edge of the dough, stretch it upward, and fold it over the center. Rotate the bowl and repeat 4 times per session to build strength.
04 - Turn the dough onto a lightly floured work surface. Gently shape it into a round by folding the edges toward the center. Cover with a kitchen towel and let rest for 20 minutes to relax the gluten.
05 - Shape the dough into a tight round loaf by folding and creating surface tension. Place the dough seam side up in a well-floured proofing basket or lined bowl. Dust the top with rice flour or additional bread flour.
06 - Cover and let rise at room temperature for 2 to 3 hours until increased in volume and slightly puffy. For enhanced sour flavor, refrigerate overnight for 8 to 12 hours of cold proofing.
07 - Position a Dutch oven or heavy oven-safe pot with lid in the oven. Preheat to 480°F for at least 30 minutes to ensure thorough heating of the cooking vessel.
08 - Gently invert the dough onto a piece of parchment paper. Use a sharp blade or bread lame to score the surface with a shallow cut. Transfer to the preheated pot, cover with the lid, and bake for 20 minutes. Remove the lid, reduce temperature to 430°F, and continue baking for 25 minutes until deep golden brown with a crispy crust.
09 - Remove the bread from the pot and transfer to a wire cooling rack. Allow to cool completely for at least 1 hour before slicing to prevent the crumb from becoming gummy.