01 - In a large bowl, combine bread flour, whole wheat flour, and water. Mix until just combined. Cover bowl and let rest for 1 hour to allow flour hydration.
02 - Add active sourdough starter and sea salt to the dough. Mix by hand or spatula until fully incorporated and no dry streaks remain.
03 - Cover dough and ferment at room temperature for 4 to 5 hours. Every 30 to 45 minutes, perform stretch and folds: grab one edge of dough, pull upward, and fold over center. Repeat four times per session.
04 - Turn dough onto lightly floured surface. Gently shape into round, cover with towel, and let rest for 20 minutes to relax gluten.
05 - Shape dough into tight round loaf, creating surface tension. Place seam side up in well-floured proofing basket or bowl lined with towel.
06 - Cover and let rise at room temperature for 2 to 3 hours until increased by about 75 percent. For pronounced sour flavor, refrigerate overnight.
07 - Place Dutch oven or heavy pot with lid in oven. Preheat to 480°F for at least 30 minutes to ensure thorough heating.
08 - Gently invert dough onto parchment paper. Score surface with sharp blade or lame. 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. Transfer to wire rack and cool completely for at least 2 hours before slicing to ensure proper crumb structure.