Combine the starter, water, and 360 g of flour. Beat vigorously for 1 minute.
Cover and let rest at room temperature for 4 hours. Refrigerate overnight, for about 12 hours.
The next day, let mixture come to room temperature. Add salt and the remaining 240 g of flour. Knead to form a smooth dough.
Allow the dough to rise in a covered bowl until it’s light and airy, with visible gas bubbles. Depending on the vigor of your starter, this may take 5 hours or longer. For best results, gently deflate the dough once an hour by turning it out onto a lightly floured work surface, stretching and folding the edges into the center, and turning it over before returning it to the bowl. Adding these folds will give you a better sense of how the dough is progressing as well as strengthen it.
Gently divide the dough in half. Shape the dough into two loaves (rounds, ovals, or baguettes) and place them on a parchment-lined baking sheet. Cover and let rise until very puffy, about 2 to 4 hours. Don’t worry if the loaves spread more than they rise; they’ll pick up once they hit the oven’s heat.
Preheat the oven to 425°F. Spray the loaves with lukewarm water and slash.
Bake the bread for 25 to 30 minutes, until it’s a very deep golden brown. Remove it from the oven, and cool on a rack.
Store bread, loosely wrapped in plastic, for several days at room temperature; freeze for longer storage.