Combine the ingredients, except the salt. Mix the bread flour, starter, sugar, and water in the bowl of your stand mixer. Mix on low until all ingredients are incorporated. It will look rough and maybe a little dry. Cover the bowl with a damp, clean tea towel and let it rest at room temperature for 30 minutes. (It is helpful to measure out the salt and put it on top of the towel so you don't forget to add it in step 2!)
Knead in the stand mixer until smooth. Add the salt and knead on low for 5-9 minutes, until the dough is smooth. The dough should form a ball and clear the sides and bottom of the bowl. If it's too dry, add a bit more water, and if it's too wet, a bit more flour.
Rise until doubled. Shape the dough into a smooth ball and place in a clean, lightly oiled mixing bowl. Cover with greased plastic wrap and put in a warm place for 3-4 hours until doubled and very puffy.
Divide, shape, and rise again. Divide the dough in half and shape into 2 smooth balls by simply pulling the dough smooth from the bottom. Place into a proofing basket dusted with flour or on a baking sheet lined with parchment. Cover with greased plastic wrap and refrigerate overnight, or up to 18 hours.
Bake. In the morning, preheat the oven to 425 degrees with an empty Dutch oven inside. Slash with a lame or serrated knife. Place the loaf on a piece of parchment and carefully lower it into the hot Dutch oven. Put the lid on and bake for 25 minutes with the lid on, then remove it and bake 20 minutes with the lid off, until very deep golden brown.
Cool and slice. Remove the loaf and place on a cooling rack for 4 hours before slicing. Store at room temperature for up to 4 days.