Take starter out of the refrigerator.
Add: 75 grams water
75 grams bread flour
Stir, and leave on counter for 2-3 hours or until bubbly and active.
In a bowl, add:
350 grams water
150 grams active starter
Stir, then add:
500 grams bread flour
11 grams sea salt
Using rubber scraper, fold and turn until all flour is moistened. Cover bowl with a plate and let rest on the counter for 1 hour.
Do an envelope fold and cover to rest another 30 minutes-1 hour.
Repeat envelope fold, cover, and put in refrigerator until ready to use, at least 12 hours.
Remove bowl from refrigerator, scrape dough out onto an olive-oiled surface. Dimple and envelope fold. Return to bowl, cover, and let rest 30-45 minutes or until room temperature.
Smooth and form into tight boule shape and place top down into floured banneton. Cover with tea towel and let rise until 1 ½ times size, about 2-3 hours. When bread has risen, place Dutch oven in the oven and turn on to 475°.
When oven is fully preheated, gently turn dough out onto olive-oiled surface. Score and drop into preheated Dutch oven with lid on. Cover and bake for 25 minutes. Then remove Dutch oven lid, turn oven down to 325°and continue baking for 15-20 minutes until golden brown.
Remove from Dutch oven immediately and cool on rack.