Mix together the flour and the salt in a large bowl.
Add the sourdough to the water and mix well (here's a hint: your sourdough is good if it mostly floats on the top). If you are using yeast and not sourdough, sprinkle it overtop of the water and allow it to sit for about 5 minutes to "bloom."
Make a well in the dry ingredients, and pour the water/yeast mixture into it.
Begin to mix the bread together, first with a spoon, but you'll probably need to get in there with your hands to really mix it together until all the flour is incorporated.
Cover with plastic wrap and a tea towel, and allow to sit in a warm spot overnight.
The next morning, remove from the bowl. It should have grown significantly overnight, if not doubled in size. Trace the shape of the lid of your dutch oven on a piece of parchment, and cut that circle out. Place the parchment on a cutting board. Form the dough into a nice circle loaf (you may need to flour your hands and your work surface if the dough is sticky) and place it on the parchment. Cover with a damp tea towel and allow to sit in a warm place to rise for 45 minutes.
After 45 minutes, place your dutch oven in the oven, and turn the temperature on to 450 degrees. Allow the oven to preheat for 45 minutes.
Once the oven and dutch oven are hot, carefully pull the loaf up and drop it into your pot. Cover and allow to bake for 30 minutes.
Remove lid, turn down the heat to 400 degrees, and bake an additional 15 minutes. Remove from oven, allow to cool and enjoy (preferably still warm, with olive oil or vegan butter).