Feed your starter: The night before baking, feed your sourdough starter. It should be bubbly and doubled in size when ready to use (usually 8-12 hours after feeding).

Mix the dough: In a large bowl, combine 100g active starter with 350g water and stir until dissolved. Add 400g bread flour and 100g whole wheat flour, mixing until no dry flour remains. Cover and let rest for 30 minutes (this is called the autolyse).

Add salt: Sprinkle 10g salt over the dough and incorporate by gently folding and squeezing the dough. Cover and begin bulk fermentation.

Bulk fermentation with stretch and folds: Over the next 3-4 hours, perform a series of stretch and folds every 30 minutes for the first 2 hours.

Pre-shape: When the dough has increased in volume by about 50% and feels puffy with visible bubbles, gently turn it onto a lightly floured surface. Form into a rough ball and let rest for 20 minutes.

Final shape: Flip the dough over and shape into a tight ball by dragging it toward you on the counter. Place the shaped dough seam-side up in a floured proofing basket or towel-lined bowl.

Cold proof: Cover the basket and refrigerate for 12-14 hours (overnight).

Preheat: The next day, place your Dutch oven in the oven and preheat to 500°F (260°C) for 1 hour.

Score and bake: Turn the dough out onto parchment paper. Score the top with a deep slash. Transfer the dough on the parchment into the hot Dutch oven, cover, and bake for 20 minutes.

Reduce heat and finish: Lower the temperature to 450°F (230°C), remove the lid, and bake for another 20-25 minutes until deep golden brown.

Cool: Remove the bread from the oven and cool completely on a wire rack (at least 1 hour) before slicing.