Combine flour, water, starter, and salt in a bowl. With a dough whisk or your hands, mix until uniform.
Let rest for 20-30 minutes, then give a series of stretch and folds.
If using add-ins, add them to the dough now (i.e. after the first stretch and fold). Incorporate the add ins by stretching and folding the dough at 30 minute intervals for another 2 or 3 times. As you stretch and fold, the dough will become more elastic and smooth and strong and the add-ins more evenly incorporated,
If not using add ins, you should perform a total of 2-4 stretch and folds at rough 30 minute intervals.
Let dough rise for 4-8 hours (or overnight). The dough should have almost doubled.
Prepare your banneton by dusting liberally with rice flour. If your banneton has a cotton covering, the rice flour should be rubbed into the cotton.
Tip the dough onto the counter and form it into a round or oval shape (depending on your banneton). Transfer the dough seam side up into the banneton. If the seams open up, stitch them together by pulling the seams into the center and pinching slightly.
Let the dough proof in the banneton until puffy. When you poke the dough, it should take a long time (30 s) to bounce back. Alternatively, you can let the dough cold-proof in the refrigeration for up to 2 days after shaping and placing in the banneton.
Place your dutch oven inside your oven and preheat the oven to 450 F.
Once heated, remove the dutch oven. Remove the top of the dutch oven. Tip the dough from the banneton over onto the bottom of the dutch oven. Score the dough with a bread lame or a sharp knife.
Bake for 20 minutes, covered. Then bake uncovered for another 20 minutes, or until golden brown and the bottom of the bread makes a hollow sound when tapped.
Let cool completely before slicing.