Mix starter and water with a fork until distributed. Add flours. Mix with fork until dry, then finish incorporating flours with hands until no flour streaks remain.
Let rest, covered with a damp cloth, for 45 minutes. This is the autolyse stage.
When autolyse is complete, add salt and squeeze liberally into dough. Mix dough with your hands for 3 minutes, kneading and really working the salt into the dough. Then perform your first set of stretch and folds. Let rest for 30 minutes, and repeat set of stretch and folds. Do this 2 more times, for a total of 4 sets of stretch and folds.
When that is finished, let dough rest, cover bowl with a damp cloth and let dough rise until just about doubled, but not quite. You will see some small bubbles around the edges of the top of the dough, and it will be a bit domed, and tiny bubbles all throughout the inside of the dough when you look at the sides of the bowl. This is when bulk fermentation is complete. With my house at 70 degrees F, this took about 4 hours from the last set of stretch and folds.
Gently move dough onto a lightly floured surface. Let rest for 15 minutes, covered. Then shape your bread and use a bench scraper to put dough into banneton, seam side up. and put into a banneton. (You can use an oval or round banneton.)
Cover with a plastic bag, and refrigerate for 8-12 hours. The longer it stays in the refrigerator, the more tang (sour) you will get from the loaf.
Preheat oven to 450 degrees F, with your dutch oven in it. When oven is preheat, remove dough from refrigerator and score according to your preference. Bake for 20 minutes with lid on, then remove lid and turn heat down to 425 degrees F and bake for additional 20-25 minutes, until crust is golden brown.
Remove from oven and place on cooling rack. Let rest for one hour before slicing.