Take a potato, peel and boil till soft entirely to center 45 +mins.
 Pour liquid in ball jar quart looks right
Let liquid cool
mash potato cooled
Add 1/2 potato to water
Cover top of ball jar with cheese cloth , and use rubber band or something to keep cheese cloth secure
Store in cool, dark place for 48-72 hrs
Use 250 ml of your new starter for 3 cups of flour
Add flour slowly while mixing 
add extra de-chlorinated water as needed for dough (Depends on the flour)
Boil another Potato same as above, add some of the water and mashed potato to your starter
Replace cheese cloth with l Ball jar lid , very loosely so it can let air out as it bubbles
Keep in fridge till needed.