In a jar, mix the 20g starter, 40g white flour, 10g rye flour, and 50g water. Cover loosely and leave at room temperature until it triples in volume, is highly bubbly, and domed on top. (Note: This makes 120g of levain. You will use 100g and have 20g left over to feed as your ongoing starter).

Place a large bowl on a digital scale. Whisk together the 375g water, 100g active levain, and 12g salt until milky. Add the 450g white flour, 25g rye, and 25g wholemeal. Mix with a dough scraper or your hands until a rough, shaggy dough forms with absolutely no dry spots.

Wet your hands. Grab the dough from the middle, lift it up so the ends hang down, and fold it in on itself to roughly shape a ball. Cover the bowl with a damp towel and rest at room temperature for 30 minutes.

After 30 minutes, wet your hands. Grab the dough, slap the bottom end against the counter, and fold the top over toward you. Give it a quarter turn and repeat 2 or 3 times until the dough feels tight and resists stretching. Place it back in the bowl, cover, and rest 30 minutes. Repeat this exact folding and resting process 3 more times. 5. Bulk Fermentation (Watch the dough, not the clock)

After your final fold, cover the bowl and let it sit at room temperature (24°C–27°C / 75°F–80°F). Do not let it double in size. The bulk ferment is finished when the dough has risen by roughly 75%, is visibly domed on top, and jiggles like set gelatin when you shake the bowl.

Turn the dough onto a lightly floured surface. Fold the top down to the middle, fold the sides into the center, and tightly roll it from top to bottom into a log. Drag it gently toward you to create surface tension. Place it seam-side up into a proofing basket heavily dusted with rice flour. Pinch the seam shut, seal the whole basket in a plastic bag, and refrigerate for 12 to 24 hours.

Leave the dough in the fridge. Place your Dutch oven (with the lid) into the oven and preheat to 250°C (480°F) for one full hour.

Once the oven is screaming hot, take the dough out of the fridge. Gently poke it with a floured finger. If the indent springs back slowly and stops halfway, it is ready. Turn the dough out onto a piece of parchment paper. Using a sharp razor (lame), make one confident, deep score (about ½ inch) down the center at a slight angle.

Use the parchment paper to carefully lower the dough into the hot Dutch oven. Put the lid on and bake covered at 230°C (445°F) for 20 minutes. Remove the lid, drop the temperature to 200°C (390°F), and bake uncovered for another 20 to 25 minutes until deeply browned.

Transfer the loaf to a wire rack. Let it cool for at least 2 full hours before slicing to prevent a gummy crumb.