01 - Combine bread flour, whole wheat flour, and water in a large mixing bowl. Mix until just incorporated and no dry streaks remain. Cover the bowl with a damp towel and let rest at room temperature for 1 hour to hydrate the flour.
02 - Add the active sourdough starter and sea salt to the autolyse mixture. Mix thoroughly by hand using a pinching motion or use a spatula until the starter is fully distributed and salt is dissolved throughout the dough.
03 - Cover the bowl and let the dough ferment at room temperature for 4–5 hours. Every 30–45 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 develop gluten strength.
04 - Turn the dough out onto a lightly floured work surface. Gently shape it into a round boule, folding the edges toward the center to create surface tension. Cover with a towel and let rest for 20 minutes to relax the gluten.
05 - Shape the dough into a tight round loaf, creating a taut surface. Place the dough seam-side up in a well-floured proofing basket or bowl lined with a heavily floured kitchen towel.
06 - Cover and let the dough rise at room temperature for 2–3 hours until increased in volume by about 50%. Alternatively, refrigerate overnight for 12–16 hours for enhanced sour flavor development and easier handling.
07 - Position a Dutch oven or heavy oven-safe pot with its lid on the center rack. Preheat the oven to 480°F for at least 30 minutes to ensure the vessel is thoroughly hot for optimal oven spring.
08 - Gently invert the dough onto a piece of parchment paper. Use a sharp blade or bread lame to score a shallow slash across the surface. Transfer the dough into 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 hollow sound when tapped on the bottom.
09 - Remove the bread from the pot and transfer to a wire cooling rack. Allow to cool completely for at least 2 hours before slicing to prevent the crumb from becoming gummy and to allow flavors to fully develop.