Combine 2 cups flour, 2 cups warm water and contents of the packet in a room temperature or slightly warm bowl. Use a wooden or plastic spoon to stir the mixture until smooth.
Cover the container with plastic wrap and place it in a warm, draft free area (80-85°F) for 24 hours. Stir at least twice during this period; starter will be bubbly and give off a yeasty, sour aroma. The consistency should be similar to a pancake batter.
Cover sourdough container and place in refrigerator for 24 hours before using.
Using the Starter
Refresh the sourdough the day before you want to use it in your recipe (8-12 hours before use). To do this, remove from refrigerator and allow to reach room temperature. Measure out 1 1/2 cups of starter into a room temperature or slightly warm bowl and return the remaining starter to the refrigerator.
Add 1 1/2 cups of flour and approximately 1 cup of warm water (85°F) and mix well. The mixture should be the consistency of pancake patter. Cover the bowl to prevent drying and let the mixture proof for 8-12 hours in a warm place.
When the mixture is properly proofed, the surface will be bubbly and it will exhibit a strong, pungent and sour odor.
After proofing, measure out the amount called for in your recipe and return the remaining mixture to the original container. Stir and keep refrigerated.