My go-to simple sourdough recipe is adapted from King Arthur Flour, and uses no commercial yeast. A slow overnight rise helps develop the flavor. Adding steam to the oven while you bake helps the bread to achieve maximum expansion and eventually a crisp, golden-brown crust (to get really knitty gritty: It liquefies the starches on the outside, helping to form a nice crisp crust, while keeping it from getting too dark before the bread cooks all the way through—ensuring you get a nice, golden brown exterior.) —Laura Sant
Mix together the starter, water, and 3 cups of flour in a bowl until fully incorporated. Loosely cover and let rest in a warm place for 4 hours. Transfer to the fridge and let rest overnight.
Twelve hours later, add the remaining dry ingredients and knead until incorporated. Cover and let rise until light and bubbly, from 3 to 5 hours, folding the dough once an hour by stretching the edges into the center and turning it over.
Divide the dough in half and shape into two loaves on a baking sheet lined with parchment. Cover loosely with lightly oiled plastic wrap and let rise until puffy (2 to 4 hours). Toward the end of proofing, preheat the oven to 425º F with a cast-iron skillet on the bottom rack. Prep a cup of very hot tap water.
Score your loaves and add them to the oven. Quickly (and carefully; steam burns hurt!) pour the hot water into the cast-iron skillet and close the door. Bake for 25 to 35 minutes, until golden brown.