Method

1. Feed your starter — about 5 hours before you plan to mix. Feed it so it can double in size and turn bubbly and slightly domed on top by mixing time. Measure out the water now too, and let it sit at room temperature so it isn't too cold when you mix.

2. Mix water, starter and flour. Combine the water, starter and both flours. You don't need to knead aggressively — just make sure everything is evenly mixed with no dry spots. Cover and let it rest.

3. Add the salt — roughly 30 minutes after mixing. Sprinkle it in and gently work it into the dough by squeezing and folding.

4. Begin folding the dough — about 30 minutes after adding the salt. Perform a series of folds every 30 minutes for about 2 hours (4 sets total). Each time, start at one side, grab the dough, stretch it upward, and fold it over itself. Rotate the bowl and repeat on all sides. After the last fold, let the dough rest undisturbed until preshape time.

5. Preshape — a few hours later, once the dough has visibly risen and feels airy. Turn it out onto a clean, dry (non-floured) surface. Preshape using your hands or a bench scraper, building surface tension into a smooth, tight round. See this video if needed, then let it rest.

6. Shape and refrigerate — about 30 minutes after preshaping. Lightly flour the top of the dough, then flip it upside down. Stretch it gently into a rectangle and fold it like an envelope. Cross-fold the sides, then roll it up tightly. See this video if you're unsure about the technique. Place the dough seam-side up in a floured proofing basket, then refrigerate overnight.

7. Bake the next day. Preheat your oven to 230 °C (top and bottom heat). Score the dough and bake for about 20 minutes with steam, then another 20 minutes without steam, until the crust is golden brown and the internal temperature reaches around 96 °C. If your oven doesn't have a steam function, add a small tray of water or a few ice cubes on the bottom shelf during the first 20 minutes.