Mix: Combine all ingredients in a large bowl and stir until roughly incorporated. Knead: Turn onto a clean work surface and knead until a smooth dough forms. It will be sticky! As the gluten forms through kneading, it will soften up and stick less. Avoid adding too much flour - just a light dusting if you really need it. The end goal here is a smooth ball of dough that can hold its own weight. To test, pick up the whole ball of dough by a handful and hold it up. If it lasts a good 5 seconds before any tearing, kneading is done. This usually takes me about 15 minutes. Prove: Form the dough into a loose ball and place in a bowl. Cover loosely and prove at room temperature for 2-3 hours, until doubled in size.Shape: Turn dough out onto a lightly floured surface. Knead the dough lightly a few times. Shape into a disc, fold it in half, turn 90 degrees, and repeat until you've gone all the way around the dough. Place seam-side down and cup your hands around the far side of it. Pull your hands gently toward yourself so the dough is pulled along the worksurface. You should feel the tension in the surface of the dough building. Turn 90 degrees and repeat until your dough is in a firm ball with the seam at the bottom. Prove: Place a tea towel in a large bowl and flour generously. Place the shaped dough seam-side up in the prepared bowl. Prove 3 hours - up to overnight - until the dough is roughly doubled in size. Score + Bake: Place a baking dish with 1-inch of water in it on the bottom rack of the oven. Place a cast iron skillet on a rack in the middle of the oven. Preheat oven to 450 degrees. Once preheated, remove the cast iron skillet and turn the prepared dough into it (it should be seam-side down now). Score with a sharp knife and return to the oven. Bake for 30-40 minutes, until crisp and the bread sounds hollow. Remove to a cutting board or wire rack and cool for an hour.
I always use my kitchen scale when making sourdough. The volume measurements listed are calculated based on weight-to-volume conversions of each specific ingredient. At this time, I have not tested this recipe using the volume measurements listed. Keep in mind that if you are using a different type of flour - in either your starter or your bread - the volume equivalent to the listed weight may be different.