Combine 500 g Caputo Manitoba Oro flour and 390 g filtered water in the mixer bowl. Mix on low speed just until incorporated. Rest for 5 minutes.
Increase speed to medium-high and mix for 5 minutes. Rest again for 5 minutes.
Add 100 g levain and 12 g sea salt. Mix on high until dough stops sticking to the sides and reaches about 82°F (28°C).
Transfer dough to a shallow container and keep it warm (around 82°F (28°C)—I put it in my oven with just the light on).
Perform three sets of coil folds, spaced 30 minutes apart.
Once dough has risen about 30-40%, shape into boule or bâtard. Don't wait for a larger rise—since the dough is warm, it'll continue proofing in the refrigerator.
Cold ferment for 18 hours.
Preheat oven with a Dutch oven inside to 480°F (~250°C). Allow at least 30 minutes after reaching temperature to ensure even heat.
Transfer dough to parchment paper, score, and place in Dutch oven. Bake covered for 25 minutes.
Reduce heat to 425°F (~220°C) and open oven door to release heat. Remove lid of Dutch oven and bake another 25 minutes or until deeply golden.