01 - In a large bowl, mix bread flour, whole wheat flour, and water until just combined. Cover and rest for 1 hour.
02 - Add sourdough starter and salt to dough. Mix by hand or spatula until fully incorporated.
03 - Cover and ferment at room temperature for 4-5 hours. Every 30-45 minutes, stretch and fold dough in bowl 4 times.
04 - Turn dough onto lightly floured surface. Shape gently into round, cover, and rest 20 minutes.
05 - Shape dough into tight round loaf. Place seam side up in well-floured proofing basket or bowl.
06 - Cover and rise at room temperature 2-3 hours, or refrigerate overnight for pronounced sour flavor.
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, bake 20 minutes. Remove lid, reduce to 430°F, bake 25 minutes until deep golden brown.
09 - Remove bread from pot. Cool completely on wire rack before slicing.