01 - In a large bowl, combine bread flour, whole wheat flour, and water. Mix until just combined, cover, and let rest for 1 hour.
02 - Add sourdough starter and sea salt to the dough. Mix by hand or spatula until fully incorporated.
03 - Cover and ferment at room temperature for 4-5 hours. Perform stretch and folds every 30-45 minutes, repeating 4 times throughout fermentation.
04 - Turn dough onto lightly floured surface. Gently shape into a round, cover, and let rest for 20 minutes.
05 - Shape dough into a tight round loaf. Place seam side up in a well-floured proofing basket or bowl.
06 - Cover and let rise at room temperature for 2-3 hours. For more pronounced sour flavor, refrigerate overnight for cold proofing.
07 - Place Dutch oven or heavy pot with lid in oven. Preheat to 480°F for at least 30 minutes.
08 - Gently invert dough onto parchment paper. Score surface with sharp blade. Transfer to preheated pot, cover, and bake for 20 minutes. Remove lid, reduce temperature to 430°F, and bake 25 minutes until deep golden brown.
09 - Remove bread from pot and transfer to wire rack. Cool completely before slicing for optimal texture.