Classic Sourdough Starter

In a bowl, whisk together the water and yogurt. Add the flour and dry milk powder and beat until well blended and smooth. Transfer the mixture to a 1-quart glass jar, ceramic crock or plastic container. Cover loosely with plastic wrap or a double thickness of cheesecloth and let stand at room temperature for 48 hours, stirring the mixture with a whisk twice each day. It will be bubbly, with a fresh sour smell and the consistency of pancake batter. A clear or pale yellow liquid will form on the top; just stir it back in. If the liquid is any other color (such as pink or green), discard the starter and make a new batch. Cover loosely with plastic wrap and store in the refrigerator.

To use the starter, measure out the amount called for in a recipe and let stand at room temperature until it starts to bubble, about 1 hour. To feed the remaining starter, add 1 cup flour and 1 cup water, stir to incorporate, and let stand at room temperature for 24 to 48 hours to begin fermenting again. Store in the refrigerator, covered loosely. Makes 3 cups.

Adapted from Williams-Sonoma Collection Series, Bread, by Beth Hensperger (Simon & Schuster, 2002).