Add the warm water to a crock jar that holds at least 1 gallon. This will prevent the starter from frothing over while it’s setting up.
Whisk in the yeast and sugar and let sit for 1 minute.
Slowly whisk in the flour. You want the consistency like a thin pancake batter, so adjust the water and/or flour if necessary.
Drop the potato pieces into the bottom of the crock jar. Cover with a tea towel and let sit on the counter for at least 12 hours, stirring halfway through. You can let the starter sit for 24 hours for a more sour flavor.
Before using the starter in a recipe, whisk it briskly until smooth.
Notes
The starter will be sourest with its first use, so you may want to add a little more sugar to the first recipe you use it in. I typically keep this starter for a week at a time, stirring at least once a day. However, you can keep it as long as the potato stays intact. I prefer to use a russet potato because it holds up the best, but you can use any potato you have on hand. Always cover the starter with a towel and never refrigerate it.Recharging the starter 1 1⁄2 cups warm water 1 1⁄2 cups all-purpose flour 1 1⁄2 tablespoons sugar When you have used 3 cups of the starter, whisk all the ingredients into the jar. The starter is ready to use again, or you can let it sit for 6 to 12 hours to create a more tart taste.