01 - In a large bowl, mix the bread flour, whole wheat flour, and water until just combined. Cover and rest for 1 hour.
02 - Add the sourdough starter and salt to the dough. Mix by hand or spatula until fully incorporated.
03 - Cover and let ferment at room temperature for 4-5 hours. Every 30-45 minutes, stretch and fold the dough in the bowl 4 times.
04 - Turn the dough onto a lightly floured surface. Shape it gently into a round, cover, and let rest for 20 minutes.
05 - Shape the 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, or refrigerate overnight for a more pronounced sour taste.
07 - Place a Dutch oven or heavy pot with lid in the oven and preheat to 480°F for at least 30 minutes.
08 - Gently invert the dough onto parchment paper. Score the surface with a sharp blade. Transfer to the preheated pot, cover, and bake for 20 minutes. Remove lid, reduce temperature to 430°F, and bake another 25 minutes until deep golden brown.
09 - Remove bread from pot. Cool completely on a wire rack before slicing.