Step 1

Place the warm water in a small bowl, and sprinkle the yeast over the top. Let stand until yeast has dissolved and is foamy, about 15 minutes.

Step 2

Measure flour into a large bowl. Make a well in the center, and pour in the yeast mixture and cold water. Use a sturdy spoon to mix it together until sticky and difficult to stir, but nevertheless thoroughly combined. Cover and allow to ferment for 24 hours in the refrigerator before using.

Step 3

Store in the refrigerator for up to 2 weeks. To use, rinse a measuring cup in cool water, scoop out the amount of starter needed, and bring to room temperature.