This section is from the book "The White Ribbon Cook Book", by Kathryn Armstrong. Also available from Amazon: The White Ribbon Cook Book.
Sponge, a pan of buttermilk, or sour milk, flour, 1 teacupful of yeast.
For the sponge take a pan of buttermilk or sour milk which has just turned thick. Put it on the stove and scald. When the curd is well separated from the whey strain or skim it out. Let the whey cool until it will not scald, then stir in the flour, beating thorougly. It should be about as thick as batter for griddle cake. Sweet milk, or even water, may be used as a wetting for the sponge, if good sour milk or buttermilk cannot be had. But fresh buttermilk is, perhaps, the best of all. When the sponge is about milkwarm, beat in a teacupful of yeast. One teacupful of the yeast is enough for three ordinary white loaves, one loaf of brown bread and a tin of rolls. The sponge should be made at night. Let it stand until morning. Unless the weather is very cold, it is not necessary to put it near the fire. In the morning, when the sponge is light, take out enough for your loaf of brown bread. Mix the remainder with flour, taking care not to put in too much, as that will make the bread dry and hard. Knead 1/2 an hour. The whiteness and delicacy of the bread will be much increased by thorough kneading. Put the dough away to rise again. When it is light, if you wish to make rolls, save enough of the dough for that purpose. Make the remainder into loaves. Set them away to rise. When light, bake.
 
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