In a large bowl, combine the all-purpose flour, whole wheat flour, and water. Mix either with your hands or a Danish dough whisk until combined. Cover with a damp towel and allow to sit for 30 minutes.

Add sourdough starter and salt to the flour mixture. Mix with your hand for 5 minutes. Using a wet hand can make this somewhat less messy.

Cover with a damp towel and let rest for 30 minutes.

Begin the stretch and fold process. Stretch and fold the dough 5-8 times (until you notice resistance from the dough). Do this for three cycles in 15-minute intervals. Cover with a damp towel between cycles.

Increase the stretch and fold cycles to every 30 minutes. Complete three cycles of stretch and folds. Cover with a damp towel between cycles.

After all stretch and fold cycles are complete, cover with a damp towel and allow to rest on the counter for 5-6 hours or until doubled and domed on top. I’ve found that any space below 73 degrees slows down the process, so find a warm place or use a proofing box.

Once the dough has doubled and is domed on top, turn it out on a clean counter or work surface.

Use a bench scraper to divide the dough into 8 equal portions.

Shape each portion into a ball by turning it clockwise while simultaneously pulling it toward yourself on the countertop. The friction on the dry counter will create tension and aid in shaping.

Allow to rest for 15-20 minutes.

Meanwhile, prepare 8 small bowls for cold proofing. Line each bowl with a towel and generously flour the towel (I used cereal bowls lined with clean dishtowels).

Use a bench scraper to transfer the dough to the bowls FACE DOWN (sprinkling a little water on the bench scraper and your hands can prevent sticking).

Gently pinch the left and right sides together. Then, pinch the top and bottom together. This creates tension and a nice seam.

Cover each bowl with plastic (I used plastic wrap) and refrigerate for 12-15 hours.

With the filled dish in the oven, preheat the oven to 450° F.

Line a large baking sheet with parchment paper.

Turn out each dough ball onto the baking sheet. Note: you may have to bake in batches. I can only fit 6 bread bowls on my baking sheet.

Use a bread lame or razor to score an "X" in each dough ball.

Bake at 450° F for 20 minutes.

Drop the temperature to 425° F and continue baking for another 20 minutes or until the bread reaches an internal temperature of 190° F.

Remove the bread bowls from the oven and transfer them to a wire rack to cool. Allow them to cool completely to room temperature before digging in.

Once you are done baking, let the water and dish cool in the oven. Then, remove it from the oven.