(Autolyse) In a large bowl, mix together 400 grams of flour and 320 grams of water. Stir until no dry flour remains. Cover and let rest for 30–45 minutes.
Add 100g active sourdough starter and 10g (1 ¾ teaspoons) salt. Mix thoroughly using a wooden spoon, or a Danish dough whisk. This is a pretty wet dough and will be sticky. This is expected with its hydration level. Let the dough rest at room temp, covered with plastic wrap or a damp kitchen towel for 30 minutes.
After the 30 minutes, perform 3 sets of stretch and folds, spaced 30 minutes apart. To stretch and fold, wet hands, lift and stretch one side of the dough up, then fold it over. Rotate bowl and repeat on all four sides. (SEE TIPS) Cover the bread dough again with plastic wrap of a damp cloth and place in a warm place. Let the dough rise for about 6-8 hours, or until it has doubled in size.
After the first rise, wet hands and shape the dough into a tight round or oval shape and place it seam-side up in a generously floured banneton basket or towel-lined bowl. Cover the proofing basket with a damp towel or plastic bag and place in the fridge for 10–14 hours.
Next day, place dough seam-side down on a piece of parchment paper and into a Dutch oven. Score the top of the dough with sharp razor blade. Then cover the dutch oven with the lid. Place the dutch oven in the oven and set the oven temperature to 425°F (no need to preheat).
Bake covered for 50 minutes. If the crust has reached your desired color, remove the loaf and transfer it to a cooling rack. If a deeper color is preferred, continue baking uncovered in 5-minute intervals until the crust is golden and crisp.
Transfer to a wire rack. Let cool completely (at least 1 hour) before slicing.