Steps
1. In a mixing bowl, combine the bread flour and water. Mix until just combined and let rest for 30 minutes (autolyse).
2. Add the active levain and salt to the dough. Mix thoroughly until the dough is smooth and elastic.
3. Cover the bowl with a damp cloth and let it ferment at room temperature (around 70°F/21°C) for 12 to 16 hours, folding the dough gently every 3 hours to develop gluten.
4. After fermentation, shape the dough into a round boule and place it seam-side up in a floured banneton or bowl.
5. Cover and refrigerate overnight for a cold proof (8 to 12 hours).
6. Preheat your oven to 475°F (245°C) with a Dutch oven inside.
7. Remove the dough from the fridge, flip it onto parchment paper, score the top with a sharp knife.
8. Carefully place the dough with parchment into the hot Dutch oven, cover, and bake for 20 minutes.
9. Remove the lid and bake an additional 20-25 minutes until the crust is deep golden and crisp.
10. Cool on a wire rack before slicing.