Baking bread using the sponge method

Many years ago my sister sent me "The Tassajara Bread Book" by Edward Espe Brown. This book taught me to make bread by the sponge method. I gave the book to a friend over 10 years ago so this is my recipe and not necessarily the same as in the book but maybe it is. I love the sponge method because it's so easy to start a bread dough- no dirty hands, no kneeding, just mix everything together and let it stand. at least one hour but up to 24 hours. Often I have started my sponge in the evening and baked the next morning before work.
BREAD BY SPONGE METHOD
Sponge:
for one whole baking sheet of rolls (about 20) or one large loaf of bread or two smaller loaves
4 cups liquid. I use 2 cups buttermilk and 2 cups water. I heat my buttermilk and add cold water and then I have a liquid at room temperature.
Add 1 T. dry yeast
flour after choice so that the mixture is like porridge. I use oatmeal, rye flour and whole wheat flour. Mostly the first two at this stage. You can also add whole grains here. (I would soak them first)
Cover and let rise.
As I remember, the point of the sponge method is that the yeast develops best without salt, egg and oil which hamper its growth.
After at least one hour, (tho I always wait at least 2 hours) add olive oil (I use one large wooden spoonful which is 2-3 T) 1 T. salt and more flour to make a dough. I use whole wheat flour here. Kneed well and shape. I roll my rolls in poppy seeds or sesame seeds. Bake on a greased baking sheet. Cover with a dish towel and let rise ½ hour. Baste with water or with beaten egg. Bake ca. 30 min. at 350 F.
The varients in this recipe are what kind of liquid. Regular milk gives a more cake like bread. How much oil, which oil or melted butter for a cake like bread. Egg/eggs can be added in the second step. what kind of flour. I use all whole grain flour but white flour can be used in varying amounts for a lighter whiter bread.