In a large mixing bowl, combine 500 grams of bread flour and 10 grams of salt.
Add 400 grams of the active sourdough starter and 300 grams of water to the dry ingredients.
Mix everything together until you have a shaggy dough.
Cover the bowl and let it rest for 30 minutes to 1 hour. This step, called autolyse, allows the flour to hydrate and makes it easier to work with.
After the autolyse, perform a series of stretch-and-folds. Wet your hand, reach under the dough, stretch it up, and fold it over the top. Repeat this process several times, rotating the bowl as you go. This helps develop gluten.
Cover the bowl and let the dough bulk ferment for about 3-4 hours at room temperature. During this time, perform a set of stretch-and-folds every 30 minutes for the first 2 hours.
After bulk fermentation, lightly flour your work surface and shape the dough into a round loaf. Place the shaped dough into a well-floured proofing basket, seam side up.
Cover the basket with a clean kitchen towel and let it proof at room temperature for about 1-2 hours, or until it has visibly expanded and feels lighter to the touch.