Mix flour and water together in a quart jar.
Cover with a cheesecloth.
Leave mixture on the counter for 24 hours.
After 24 hours, add another 1/4 cup flour and 1/4 cup water to the mixture.
Leave on the counter for another 24 hours.
Continue this process until the start becomes bubbly.
After you see bubbles continue to feed for two more days and leave on the counter.
This process should take about a week.
Your start is now ready to use. If you are not ready to use it, simply cover with a lid and put in the fridge.
Make sure to feed your start at least once a week, and after every use. I like to feed mine the day before I plan to use it, to guarantee it is nice and bubbly.