Makes ~18 4-inch pancakes
Dissolve yeast in the lukewarm water (about 100 degrees). Put the dissolved yeast in a good-sized bowl and add enough flour (¾ to 1 cup) to make a thin, runny batter. Place in a small crock and cover lightly with a tea towel.
Put in a warm place to sour. Each day for 5 days add ½ cup lukewarm water and just enough flour to keep the batter the same consistency as when you first mixed it. When the batter is sour to the taste it is ready to use for making pancakes. This should be in about 5 days but may take a little longer.
To make it easy to have these pancakes whenever you want them, without waiting 5 days for the starter to sour, set aside a small quantity of the starter each time you make pancakes. Add ½ cup lukewarm water to it and just enough flour for the runny batter mentioned above. Leave it in a warm place overnight, then store in your refrigerator until you wish to make potatoes. Add enough flour and water when you begin to make the pancakes to provide a sufficient quantity of starter for the number of cakes you wish to make.
Beat the eggs until light with the milk and the sour-dough starter.
Sift together the baking soda, baking powder, salt, sugar and flour. Combine the two mixtures and blend well.
Bake on a greased griddle or in an oiled skillet, browning on both sides. (if you wish to use an unoiled skillet or griddle, add ¼ cup of melted butter to the batter.) If you like very thin pancakes, add a little more milk to the batter.