For best results use a kitchen scale to measure your ingredients instead of using a measuring cup.
Start by dissolving 3 oz of active starter with 12 2/3 oz room temperature water in a small bowl.
In a large bowl stir together 18 1/3 oz all purpose flour and 1 3/4 teaspoons salt. Add the dissolved starter to the flour/salt mixture.
Stir with a wooden spoon to combine.
Dough will be very shaggy, loose and sticky.
Cover the bowl with plastic wrap. Place bowl in a cold oven. Turn the light on and leave the dough in the oven for 12-18 hours. The dough should double in size during this time.
Get out an enameled, cast iron, dutch oven. Tear off a piece of parchment paper, spread it out on your counter and spray it lightly with a little non stick cooking spray.
Flour your work surface lightly. Gently remove the dough from the bowl and onto your floured surface. Gently pull it away from the sides of the bowl. The dough will be very sticky.
Lightly flour your hands and start kneading the dough using the palms of your hands. Knead 20 times.
Pull the dough up onto and over itself from all sides.
Flip the ball of dough over and cup it in your hands, gently turning it and pulling the top of the dough down the sides and underneath.
Once you have shaped the dough into a round ball place it on the prepared square of parchment paper.
Grab the 4 corners of the parchment paper and place the dough in the dutch oven.
Cover the pot loosely with plastic wrap.
Place the pot in a cold oven. Place a metal pan on the lowest rack in your oven. Add 3 cups of boiling water to the pan. Close the oven door and let the dough rise for a second time, for about 3-4 hours, until it doubles in size.
Dust the top of the loaf with flour.
Cut a slash down the center of the loaf about 7 inches long and 1/2 inch deep.
Place the lid on the Dutch oven and place in a cold oven. Turn on the oven to 425 degrees. After 30 minutes remove the lid and continue to bake for an additional 30-50 minutes. Check the temperature after 30 minutes.
Check the temperature with a digital instant read thermometer. Loaf is done when it reaches an internal temperature of 210 degrees and the loaf is a deep golden brown.
Place the loaf on a wire rack and allow loaf to cool for 2 hours.