In a large bowl, mix the water and sourdough starter.
Add the flour and salt and mix into a shaggy dough.
Cover and let rest for 30 minutes.
Perform 3 sets of stretch and folds every 30 minutes by pulling each corner of the dough up and into the center of the dough all the way around the bowl.
On the last and 4th stretch and fold, add 1/4 of the add ins and do a stretch and fold. Continue around the bowl adding a quarter of the add ins with each stretch and fold. Continue stretching and folding until add ins are well combined.
Cover and let rise for 4-5 hours.
Turn the dough onto a lightly floured surface.
Shape the dough by pulling each corner over and into the center of the dough. Turn the dough over and drag against the surface.
Add a tea towel to the banneton basket and flour generously.
Place the dough seam side up in the banneton basket.
Cover and place in the fridge for at least 4 hours or up to a week before baking.
Alternatively, you can let it rise on the counter for 1-2 hours and bake.
Preheat the oven to 450 degrees F with Dutch oven inside.
Carefully remove the Dutch oven.
Turn the dough onto a piece of parchment paper and score the top with a sharp knife or lame.
Carefully lift the dough into the Dutch oven and replace the lid.
Bake in preheated oven for 20 minutes.
Remove the lid and continue baking for 15 minutes.
Allow to cool completely on a wire rack before slicing.