In a large bowl, mix ¼ cup sourdough starter with 1 ½ cups of water and 1 ½ tsp sea salt.
Mix in flour and other optional add-ins like seeds or olives until well combined, about 2 minutes.
Cover bowl with plastic wrap or a plastic bag and let the dough rise at room temperature for 18-22 hours, or until it reaches almost double the size.
Once the dough has risen enough, sprinkle the top and cover your hands with more flour. Stretch and fold the dough around from the bottom to the top about 5-6 times.
Form the dough into a ball about the same size as the dutch oven you're going to bake it in, and transfer it to a parchment-lined bowl approximately the same size. Cover it with a clean towel and let it rise for another 2-3 hours.
Preheat your oven to 450°F, and place the dutch oven inside to warm it up.
Once your oven is ready, transfer dough and parchment paper to your dutch oven and score the top of the dough with a very sharp knife or razor blade to let steam escape. You can also sprinkle the top with more flour for decoration.
Bake sourdough with the lid on for 35 minutes. Then, remove the lid and bake for another 15-20 minutes until the top is golden brown.
Remove from the oven, and let the loaf cool completely on a wire rack before slicing.