In a large bowl, whisk 500 g bread flour, fine sea salt, and instant yeast. Add the water and stir firmly with a sturdy spoon, scraping the bottom until no dry pockets remain. The dough should be sticky, shaggy, and too soft for ordinary hand kneading. Cover the bowl tightly.

Allow 18 hours for bulk proofing at 65–70°F; start checking after 12 hours. The dough is ready when substantially expanded, dotted with bubbles, and webbed underneath when lifted with a spatula. Its top may flatten slightly, but it should retain visible bubbles rather than collapse into a thin puddle.

Allow 20 minutes for the bench rest. Distribute the 20 g reserved bread flour over the work surface, dough, and your hands. Scrape out the dough, fold its edges inward, and cover with the inverted bowl for the rest. Then gently tuck the edges underneath into a round and place seam-side down on oven-safe parchment.

Allow 60 minutes for the final proof, loosely covered with the inverted bowl. The round should look puffier and slowly recover from a gentle fingertip press. During the last 30 minutes, preheat the oven and a covered 5- to 6-quart Dutch oven, approximately 10 inches across inside, to 450°F. Remove the bowl before loading. Use a pot, lid, and knob rated for this temperature; preheat empty only if the manufacturer explicitly permits it. If empty preheating is prohibited, choose suitable cookware for this method.

Bake for 45 minutes total at 450°F: 30 minutes covered, then 15 minutes uncovered. Immediately before loading, slash the top about 1/2 inch deep. Carefully lower the loaf into the hot pot using the parchment. The finished crust should be deeply golden, with a center temperature of 208°F. Use dry oven mitts, set the hot lid on a heatproof surface, and lift it away from your face to release steam. Use parchment rated for 450°F and trim excess paper.

Cool for 90 minutes on a wire rack before slicing. Lift the loaf from the pot promptly, remove the parchment, and leave the bread uncovered so steam can escape. Cut with a serrated knife. Makes 12 servings, each one substantial slice, from one round loaf.