Take 2 good sized Irish potatoes, peel, and boil until done. Mash until perfectly smooth, and while hot put in 2' tablespoon fuls of sifted flour. Stir until smooth, using 1 pint of the water the potatoes were boiled in, and add flour to make a moderately thin batter. Have your yeast cake dissolving in small quantity of warm water while potatoes are cooking. When the batter is tepid, stir in the yeast cake. Set in warm place to rise. When light, it is ready for use. This yeast may be kept in closely covered jar for several days.