Using a food scale, measure out 500 grams of flour, 100 grams of sourdough starter, 425 grams of water, and 12 grams of salt into a mixing bowl. Stir together thoroughly until it makes a shaggy dough. Let rest 30 minutes.
Perform stretches & folds. Grab the edge of the dough and pull up until you get resistance, but be careful not to rip it. Fold the dough back down to the other side of the bowl. Work your way around the whole ball of dough, doing 8-12 stretches and folds. Let dough rest 30 minutes in between, and repeat this 3 more times for a total of four sets of stretches and folds with 30-min rest in between.
Right after the fourth set, transfer your dough to a clear, straight-sided container to monitor the bulk ferment. Wet the back of your hand to press down & flatten the top of a dough. Make a mark on the outside of your container to mark the dough's starting point. Assuming a dough temperature of 75 degrees F, aim for a 50% rise. Do a 75% rise if your dough is 70 degrees. Adjust rise up or down accordingly for a warmer or cooler dough.
When your dough reaches its rise target, pour dough out onto the counter and complete a pre-shape with light stretches & folds to make the dough into a ball. Using a bench scraper, turn the ball over so the smooth side is facing up. Let dough rest 20 minutes.
Use your bench scraper to turn the dough ball back over, smooth side down. Flatten the dough gently into a rectangle with your hands and shape your loaf into a batard or boule. Using your bench scraper if needed, pick your shaped dough up and place it into the banneton, smooth side down. Pinch the seam together tightly to create more surface tension.
Cover and place in the refrigerator for 8 hours (or up to 2 days).
When ready to bake, put a baking vessel, such as a dutch oven with a lid into the cold oven and pre-heat your oven to 450 degrees. When the oven is ready, pull your dough out of the fridge. Turn it out onto a piece of parchment paper or dough sling. Using a lame or sharp knife, score the dough down the middle. Pull the baking pan or dutch oven out of the oven. Remove the lid and carefully place your dough inside. Spray the top of your loaf 10 times with a water bottle, then quickly replace the lid.
Put the bread in the oven and bake at 450 degrees for 30 minutes with the lid on. Remove the lid after 30 minutes. Lower the oven temperature to 425 degrees and bake for an additional 13-15 minutes until the interior temperature of your loaf is at least 205 degrees F.
Cool on a wire rack for at least 6 hours to prevent a gummy crumb when slicing. Enjoy!
Notes
Unfed starter works for this recipe as long as your starter is generally well-maintained. But if you have better results feeding your starter before use, you can continue to do that.