Whisk starter and water in large bowl. Add flour and salt, and stir until a thick, shaggy dough forms. Cover and let rest for 20 minutes. Do first stretch-and-folds, let rest 20 minutes. Do a total of 3 series of stretch-and-folds with 20 minutes in between, then cover and let rise until at least double in size. Depending on season / temperature, this could take anywhere from 8 to 24 hours.
Do final series of stretch-and-folds, this time lifting dough from centre and letting gravity sag it down into bowl. Transfer to greased loaf pan, and put in fridge uncovered for at least an hour
Preheat oven to 500F with a tray of water in it on the lower rack. Once oven is up to temp and water is boiling, put bread in oven and set timer for 10 minutes. When 10 minutes is up, take bread out quickly and slash top with razor to allow dough to expand. Return to oven immediately, and bake for another 20 minutes. When 20 minutes is up, remove boiling water and reduce oven temp to 450F. Bake for an additional 10 minutes, then remove from oven and loaf pan and let fully cool on counter before cutting
It should look like this:
