Mix together flour, warm water, and yeast in a large glass bowl. Let stand uncovered in a warm place over night or up to 48 hours. The longer the mixture stands, the stronger the ferment will be.
After fermenting, the starter is ready to use or to store covered in the refrigerator. Feed once or twice a week with 1 cup milk, 1 cup flour, and 1/4 cup sugar; allow the starter to rest at room temperature for several hours after feeding.