Step 1

Activate your starter: Mix the unfed starter, water and all-purpose flour in a small container. Let your starter ferment until doubled or tripled in volume (about 4 to 6 hours).

Step 2

Mix your dough:In a large mixing bowl, combine water and active sourdough starter. Stir until the starter is almost completely dissolved. Fold the whole wheat flour into the starter mixture. Add all of the bread flour and salt. Stir using a wooden spoon or your hands until no dry traces of flour remain.

Step 3

Fold the dough:Complete a set of stretch and folds by picking up one side of the dough and folding it over itself. Repeat until all sides are folded. Transfer the dough to a lightly-oiled bowl, cover with plastic wrap and let the dough rest for 1 hour.

Step 4

Strengthen the dough and bulk ferment:As your dough ferments, perform 3 to 4 sets of coil folds inside the bowl at 30 minute intervals, cover your bowl with plastic wrap after you complete each fold. Your dough should appear smooth and pass the windowpane test after the last fold.

Step 5

Bench rest:After your last fold, let the dough rest for 1 hour untouched in a warm place. Your dough should look puffy and should increase in volume during this period.

Step 6

Shape the dough:Prepare your Pullman pan or loaf pan by greasing it with olive oil or butter, or lining it with a piece of parchment paper.

Step 7

Turn your dough out on a lightly-floured work surface. Lightly flatten the dough out into a rectangle (be gentle so you do not pop the air bubbles build up during fermentation).

Step 8

Fold the left and right corner of the dough towards the center.

Step 9

Fold the tip down towards the center.

Step 10

Roll the dough towards yourself into a tight cylinder.

Step 11

Pinch the ends of the cylinder. Place the dough into the prepared pan with the seam-side down.

Step 12

Cold proof:Cover the pan with plastic wrap. Place your dough inside the refrigerator and proof overnight.

Step 13

Prepare for baking:Preheat your oven to 475 F with the wire racks positioned in the middle and bottom. Place pizza stone in the middle (if using). Allow oven to heat up for at least 1 hour.

Step 14

15 minutes prior to baking, place a water pan filled with at least 1-inch of water on the bottom rack of your oven.

Step 15

Score: Take the dough out of the refrigerator, uncover and cut a long slash on the top of the dough with a sharp knife or a lame.

Step 16

Bake: Bake the dough cold directly from the refrigerator on the middle rack (on top of the baking stone, if using).

Step 17

Add ice cubes into your water pan and quickly close the door. Bake for 20 minutes.

Step 18

Remove the water pan and bake for an additional 15 to 20 minutes or until the center of the loaf registers at 190 F when probed with an instant read thermometer and the crust reaches your desired color.

Step 19

Cool: Transfer the sandwich tin to a cooling rack. Let the dough cool for at least 15 minutes before turning it out of the pan.

Step 20

Serve: Allow the loaf to cool for at least 2 hours, before slicing.

Step 21

Store: Store any leftover slices in a ziplock bag for up to 5 days at room temperature.