1/2 tsp. dry yeast
1 1/2 c. lukewarm water
2 c. flour

Soften yeast in water. Add flour and stir to mix. Put in a glass, ceramic or china container with a loose lid. (Never use a metal container for sourdough starter, and be sure it's plenty big, as the starter expands.)

Let set at room temperature for 3 days, stirring once or twice a day. The starter will "work" and will have a definite sour odor. After the starter has soured, it can be stored in the refrigerator until used.