Feed the starter 4-12 hours before starter to ensure it is active and bubbly.
In a large bowl, add flours and water. Mix until just combined. Dough will be shaggy. Let rest for 30 minutes to allow the water to hydrate the flour.
Add starter to the dough and dimple in with your fingers. Pour salt on top.
Work the dough in your hands for 5 minutes to ensure the ingredients are well incorporated. Cover with plastic wrap or a damp towel and let rest for 30 minutes.
Begin stretch and folds. The first 3 perform every 15 minutes. Then, the last 3 perform every 30 minutes.
Cover with plastic wrap or wet towel. Bulk ferment on the counter until doubled.
Gently split the dough down the middle using a dough scraper.
Shape each loaf and let sit for 15 minutes.
Do a final shaping and place seam side facing up into a lightly floored banneton or towel lined bowl.
Place in grocery bag, tie, and put in fridge to cold ferment for 12-15 hours.
The next day, preheat a cast iron Dutch oven in the oven at 500 degrees for 1 hour.
Right before baking, remove loaf from fridge and turn onto a lightly floured parchment paper. Score and place inside the Dutch oven. Bake at 500 degrees for 20 minutes with the lid on.
Remove lid and lower oven temperature to 475 degrees. Bake uncovered for 25 minutes.
Transfer bread to a cooling rack. Once cooled, slice and enjoy!
