1/2 cup lukewarm water
2 cups sourdough starter
2 1/2 cups King Arthur Unbleached All-Purpose or Unbleached Bread Flour
1 1/2 teaspoons salt
1 1/2 teaspoons granulated sugar
1 1/2 teaspoons active dry yeast
Place ingredients in bread machine in order listed and run on Dough setting (~1.5 hrs)
Remove from bread machine and shape into one or more loaves
Place the loaves on a lightly greased or parchment-lined baking sheet. Cover and let rise until very puffy, about 1 hour (may need up to 2 hrs).
Toward the end of the rising time, preheat the oven to 425°F.
Spray the loaves with lukewarm water.
Make two fairly deep (1/2 to 3/4" deep) diagonal slashes in each; a serrated bread knife, wielded firmly, works well here.
Bake the bread for 25 to 30 minutes, until it's a very deep golden brown. Remove it from the oven, and cool on a rack.