My mother wrote down this family recipe for sourdough waffles when I left for college. Improvements to the sourdough starter came from the book Cookwise: The Secrets of Cooking Revealed by Shirley O. Corriher.
Use unbleached all-purpose white flour. I am experimenting with mixes that include Semolina, Whole Wheat, or Rye Flour.
Pinches of cinnamon, cassia, ginger, and cardamon can help the dough rise. Too much may hinder the yeast.
Feed the yeast every four to six hours with equal parts dough, flour, and water (plus trace spices). Discard any excess dough. Refrigerate the dough overnight.
If cooking the waffles in the morning, feed the starter 12 to 18 hours in advance of cooking, and leave out overnight, covered.
Combine the following with each cup of sourdough used to produce waffle batter. One cup of sourdough should yield four to five waffles.
Adjust the thickness of the batter with flour or water if needed. Add the baking soda near the end.
Separate the egg whites into a different bowl, and beat until soft peaks form. Fold into the dough just before cooking. For large amounts of batter, split it into multiple bowls, and fold equal amounts of egg white into each bowl.