The evening before baking (8-10 PM), feed your sourdough starter using a 1:1:1 ratio (50g starter + 50g flour + 50g water). Place in a warm spot and let ferment overnight until doubled, bubbly, and passing the float test.
In a large bowl, whisk together warm water and active starter until dissolved. Add bread flour and sprinkle salt over top, then mix until no dry flour remains.
Cover bowl and let dough rest for 30-60 minutes at room temperature to allow flour to absorb water and gluten to begin developing.
With wet hands, perform stretch and folds by grabbing one edge, stretching upward, and folding to opposite side. Rotate bowl 90 degrees and repeat. Complete 3-4 sets total, spacing them 30 minutes apart.
Cover dough and let rise in a warm spot (75-78°F) for 3-4 hours until increased by 50-75% in volume with bubbles on surface and smooth, domed appearance.
Turn dough onto lightly floured surface, gently pull edges toward center, flip seam-side down, and use circular motions to create surface tension into a tight ball.
Place shaped dough seam-side up in a floured towel-lined bowl. Cover and proof for 1-2 hours at room temperature until puffy and slightly increased in size.
About 30 minutes before baking, place Dutch oven with lid in oven and preheat to 450°F (232°C).
Turn dough onto parchment paper seam-side down and score quickly with sharp knife at 45-degree angle, about 1/2 inch deep. Lower into hot Dutch oven using parchment, cover with lid, and bake 30 minutes. Remove lid and bake 15-20 minutes more until deeply golden (internal temp 205-210°F).
Transfer bread to cooling rack immediately and let cool for at least 1 hour before slicing to allow interior to finish cooking.