Add starter and water to a large nonmetallic bowl. Stir with a wooden spoon until well combined. Use water that is about room temperature.
Add einkorn flour, rye flour, and salt. Stir as well as you can, forming a clumpy thick dough. Cover and let rest for 30 minutes.
Wet hands and stretch and fold dough in bowl 3 times at 20 minute intervals. Add more water or flour if too wet or dry. It should be wet enough to stretch, but not so wet it is too sticky to quickly form a ball with wet hands.
After the 3rd stretch and fold, form into a ball with wet hands, cover bowl, and let ferment for a first rise at room temperature for 4 hours.
With wet hands, stretch and fold the risen dough and form into a ball. Add flour if needed. Place back into bowl, seal tightly, and place in the refrigerator to let the dough rise a second time and develop a sour flavor.
After 24 hours in the refrigerator, check dough every 12 hours to make sure it is not spoiling due to the temperature of your refrigerator. After 48-72 hours, it should develop a pleasantly sour smell.
Preheat a dutch oven in a 450 degree oven
Carefully remove dough and place in dutch oven, then cut score bread with a sharp scoring knife or other sharp utensil.
Cover with dutch oven lid and bake for 40 minutes.
Remove loaf from dutch oven and wrap in a cotton or linen cloth to prevent an extra hard crust. Allow to rest for 45 minutes before slicing.
Enjoy!
