Several hours before making the dough, feed your starter so you have at least 100 grams of active starter for the recipe plus a little left over to maintain it. For example, combine 25 grams starter, 50 grams water, and 50 grams bread flour. Stir, mark the level on the jar, and leave it at room temperature.
Let the starter rise until it has at least doubled and is bubbly and puffy, about 4 to 8 hours depending on your kitchen. Measure out 100 grams of active starter for the dough. Keep the rest to feed for your next bake.
Make the Dough
Combine the active starter and water in a large bowl. Stir to disperse.
Add the bread flour and salt. Mix until no dry flour remains. The dough will look rough and shaggy. Cover and rest 30 minutes.
Stretch and Folds
First stretch and fold. Lift one side of the dough with a damp hand until you feel resistance, then fold it over the center. Rotate a quarter turn and repeat around all four sides. Cover and rest 30 minutes.
Second stretch and fold. Repeat around all four sides. Cover and rest 30 minutes.
Third stretch and fold. Repeat around all four sides. The dough should feel smoother and more elastic. If it still feels loose, rest 30 minutes and do one more set.
Bulk ferment, covered and undisturbed, until the dough has risen 50 to 75 percent, looks puffy and aerated, has bubbles along the sides, has a slight dome, and jiggles when you move the bowl.
Turn the dough onto a lightly floured surface. For a round loaf, pull and rotate to form a boule. For an oval loaf, shape into a batard. Work gently to keep the air.
Transfer seam-side up to a well-floured banneton. Stitch the seam if needed. Cover and refrigerate overnight, 10 to 16 hours.
Bake
Preheat the oven and Dutch oven, lid on, at 450°F for 30 minutes. Remove the lid and heat 5 more minutes.
Turn the dough onto parchment straight from the fridge. Score the top. Lower into the hot Dutch oven and replace the lid.
Bake covered at 450°F for 30 minutes. Uncover, reduce to 425°F, and bake 15 to 20 minutes more until deeply golden. The center should read about 205 to 210°F.
Cool on a wire rack at least 2 hours before slicing.
Notes
Feed the starter 4 to 8 hours before mixing. It should be bubbly and active.
Use a kitchen scale. Cups are not accurate enough for sourdough.
If the dough feels loose after three folds, do one more.
Judge the rise by feel, not time. Wait for the puffy, jiggly dough.
Shape gently. Do not knock the air out.
Score the loaf straight from the fridge. Cold dough cuts cleaner.