Potato Bread – Sponge Method

From 1916:

So great is American wastefulness that housewives who really try to economize can save money even at the present high food prices. Any cook with brains can cut $1 a year from her bread bill alone and contribute her share to a possible great national saving of $20,000,000. In localities where there is a surplus of potatoes or where they are very cheap, potato bread costs less to make than all-flour bread. This would prove an excellent way in which to utilize cull potatoes. Even, however, where the relative market prices of potatoes and flour are such that there is no economy in substituting potato for flour, the individual quality of potato bread make it desirable as a variant in the family diet.

Potato Bread – Sponge Method
For four one-pound loaves are required:
Three pounds of boiled and peeled potatoes, 2 ¼ pounds of good bread flour, 3 level tablespoons of sugar, 1 ½ level tablespoons of salt, 1 cake of compressed yeast, 4 tablespoons of water.

Boil, peel and mash the potatoes. In the evening take 1 ½ pounds or 2 ½ solidly packed half-pint cupfuls of the cool, mashed potato, add to it the salt and 1 scant half-pint of flour and the yeast rubbed smooth with the water, reserving one spoonful to rinse the cup.
In the morning add the remainder of the potato, the sugar and the rest of the flour. Knead thoroughly until a smooth and very stiff dough is formed. After working the dough, set it to raise and thereafter follow the usual routine of bread making.