Mix 1 cup flour and 1 cup lukewarm water in a clean jar
Add 1/4 teaspoon active dry yeast
Stir until smooth
Cover loosely with a lid or cloth
Let sit at room temperature for 12 to 24 hours
Stir once or twice during the first day
On day 2, discard half of the mixture
Add 1/2 cup flour and 1/2 cup lukewarm water
Stir well and cover loosely again
Repeat discard and feeding every 24 hours
Keep at room temperature until bubbly and active
Use when it doubles in size within 4 to 8 hours after feeding
Store in the refrigerator and feed weekly if not using daily