For the levain

1. In a clean glass jar combine flour, water, and starter until smooth. Cover and ferment in a warm place (78F-80F) until it triples in volume. This should take about 5 hours.

For the dough

1. When there is 1 hour of fermentation time remaining for the levain, take a large bowl and add both all-purpose and whole wheat flour. Use a rubber spatula to stir in the water until a rough dough forms, with no dry bits clinging to the dough. Cover the dough with plastic wrap and let this rest for 1 hour at room temperature.
2. Using a clean wet hand scrape 65g of levain onto the dough. Use your wet fingers to evenly distribute the levain into the dough. Cup the palm of your hand and scoop the dough around the ball, ensuring that the levain has completely merged with the dough. Cover and rest for 30 minutes.
3. Sprinkle some salt all over the dough, then use wet fingers to dimple the dough. Cup your hands and mix the dough in a scooping motion. Transfer the dough to an 8-inch square baking dish, then cover the dough with plastic wrap and rest for 45 minutes. The dough should relax enough to be ready for coiling and folding. If the dough is too tough, give it some more time to relax before proceeding with the next step.

First fold

1. Wet your hands, and slide both hands beneath the right and left sides of the dough. Lift the dough ever so slightly and bring it towards you. The dough will stretch as your hands grip the bottom of it, whilst the top and bottom parts of the dough remain stuck to the baking dish.
2. Continue to lift the dough until the top and bottom release the baking dish. Once the dough is in your hands, you’ll need to dangle it so that one side of the dough touches the baking dish, then naturally folds into itself. Meanwhile, rotate the dish 180 degrees. Repeat the process with each edge of the dough, and rotate the dish 90 degrees then 180 degrees. Your dough should eventually form a nice square shape. Cover your square dough and proof it for 60 minutes at room temperature.

Second fold

1. Repeat the stretching and folding process, then cover and proof the dough for 90 minutes.

Third fold

1. Repeat the stretch and folds, then cover and proof the dough until it has increased by about 60% in size (90-180 minutes).

Shaping and bulk fermentation

1. Lightly dust your work surface with all-purpose flour, then uncover the dough and transfer it to the floured surface to prevent sticking. Dip your hands in some flour so that they don’t stick to the dough, then gently pinch the right side of the dough, stretching outwards, then gently fold it over so that the edge rests in the middle of the dough. Repeat the stretching and folding on the left side.
2. Starting from the top of the dough, use both hands to lightly stretch the dough, then roll it over to the center of the dough. Proceed to gently roll the dough towards yourself until the seam is facing the countertop and the dough is an almost perfect oval shape. Use a bench scraper to gently flip the dough, so that the seam side is facing up. Use both hands, to gently lift the dough, cradling it in your palms, then gently lay it seam side down in a pre-prepped banneton. Cover and proof the dough for 15 to 20 minutes.
3. Place the proofed dough inside a refrigerator to rest overnight for 12-16 hours.

Scoring and baking

1. Cut a 9-inch by 7-inch rectangle of parchment paper, and trim the corners till you’ve produced a roughly oval shape. Place a Dutch oven for sourdough bread in your oven, and preheat it to 485F for 45 minutes. Remove the dough from the refrigerator, uncover and place the prepared parchment paper over the banneton. Use both hands to flip the banneton so that the dough drops out and onto the parchment paper.
2. Carefully remove the preheated Dutch oven from the heated oven, and place it on a heatproof surface. Use a bread lame or sharp knife to make one long ½ inch deep slash running the length of the dough. Carefully pick up the dough, and slide it into the Dutch oven.
3. Cover and bake bread for 25 minutes, then remove the lid and cook uncovered at 450 degrees F for a further 20 minutes. Once baked, remove the sourdough loaf from the oven, and place it on a cooling rack. Do not slice the bread until it has cooled down completely, this can take up to 2 hours.