In a large bowl combine the water and sourdough starter. Stir until the starter dissolves.
Add the strong bread flour and mix until a shaggy dough forms and no dry flour remains.
Sprinkle the salt over the dough and mix again until fully incorporated.
Cover the bowl and let the dough rest for 30 minutes at room temperature. This allows the flour to hydrate and begins gluten development.
First stretch and fold:
With slightly wet hands, grab one side of the dough, stretch it upward about 6-8 inches (15-20 centimeters), and fold it over the center. You can also use a plastic dough scraper for this. Rotate the bowl and repeat until all four sides are folded.
Cover and rest for 30 minutes.
Second stretch and fold:
Repeat the same stretch-and-fold process.
Cover and rest for 30 minutes.
If you have any inclusions (vegan cheese, scallions, etc) you can add them here (ensuring you add is no more than 60 to 80 grams total).
Shape the loaf:
Lightly flour the counter and turn out the dough. Gently flatten it slightly, then fold the edges toward the center to form a round. Flip it seam-side down and tighten the surface by gently pulling the dough toward you across the counter a few times.
The dough should form a smooth, slightly tight ball. You'll know it's ready when you gently touch the top and it springs back quickly and there are a few little bubbles on top.
Cold proof:
Place the dough seam-side up into a lightly floured bowl or proofing basket. I like to stitch any pieces together but it isn't necessary.
Cover well and refrigerate for 12-18 hours. The dough will slowly ferment and develop flavor.
Bake:
Place a Dutch oven (4 quart/24 centimetres) with lid into the oven and preheat to 450ºF (230ºC) for 45-60 minutes.
Turn the cold dough onto parchment paper seam-side down. Give it a nice deep store on the top with a sharp blade. Carefully transfer the dough into the hot Dutch oven.
Cover with the lid and bake for 30 minutes.
Lower the temperature to 375ºF (190ºC). Remove the lid and bake for another 15 minutes until the crust becomes deep golden brown.
Transfer the bread to a rack and let it cool at least 1 hour before slicing.
Notes
Use bread flour. It has more protein (gluten), which is important for any yeast bread.
Notes on the starter. Wake up your started (by feeding it) and let it sit for ~4-8 hours before using. I also encourage you to use a mature started (at least 3 weeks old) for the best results.
Weigh your ingredients. Using grams is much better when baking bread, as precision is key.
Don't refrigerate too long. Chilling the dough for more than 24 hours will cause it to over-ferment for a weaker structure and and an overly sour flavour.
Size expectations. Finished loaf is a small-to-medium artisan boule, roughly 7-8 inches wide and 3-4 inches tall.
Storage. Store sourdough bread in a bread bag for up to 3 days on the counter or slice the bread, transfer it to a freezer bag, and store for up to 2 months in the freezer. Thaw at room temperature.