In a large bowl, mix sourdough starter and water until evenly mixed.
Add flour and salt, stir until all dry flour is incorporated.
Knead for 10-15 seconds to bring mixture into a cohesive mound.
Cover and let rise on the countertop for 12-24 hours, or in an oil-sprayed ziploc bag.
Shape the dough into a loaf once it has doubled in size.
Let the dough rise for another 2-4 hours, or until double in size.
Preheat the oven to 500F/260C with Dutch oven inside.
Score the dough, transfer it into the hot Dutch oven, then bake at 425F/220C for 30 minutes covered, 15 minutes uncovered, or until deeply browned.
Cool fully before slicing.