In a small bowl, combine 3 tablespoons instant potato flakes, ½ cup sugar, 1 cup warm water and yeast.
Cover loosely and let sit on the counter for 2 days, stirring daily.
After two days, add 3 tablespoons instant potato flakes, ½ cup sugar, and 1 cup warm water to the starter. Mix well.
Cover loosely and leave on counter for 8-12 hours. Refrigerate for 3-5 days.
Subsequent Feedings
Remove from fridge and stir well. Remove 1 cup of the starter to bake with immediately. Give away or discard all but 1 cup of the remaining starter.
Feed the starter with 3 tablespoons instant potato flakes, ½ cup sugar, 1 cup warm water. Cover loosely and leave on counter for 8-12 hours. Refrigerate for 3-5 days.
Repeat the above steps ("Subsequent Feedings") for as long as you'd like to keep your starter going.