How to make starter (normal flour is fine): https://youtu.be/ZDvlHcH4pcM?t=29
445 g water
700 g white bread flour
160 g active sourdough starter
18 g salt
Take 40 g sourdough starter from fridge
Add 40 g water, mix and stir
Add 20 g rye flour + 20 g wheat flour, mix and stir
Wait a few hours, until gas bubbles form
Add an additional 40 g water, mix and stir
Add another 20 g rye flour + 20 g wheat flour, mix and stir
Autolyse white flour: add 700 g white bread flour to 445 g warm (75 deg) water, let it sit covered by plastic or a lid for 30 min – 3 hr
Add 18 g salt and 160 g sourdough starter to the autolysed mixture of flour and water. Knead by hand, or with a stand mixer until dough is elastic and smooth.
Cover dough with plastic or a lid, place it somewhere warm, and allow it to ferment for 1 hour
Stretch and fold. Cover and allow it to ferment for another 1 hour.
Stretch and fold. Cover and allow it to ferment for another 1 hour. If it’s getting puffy, shape the dough. If it’s not yet puffy to your liking, continue fermentation.
Shaping the dough: push the dough ball under itself, and rotate, until the dough is shaped into a uniform and smooth ball. Place into a parchment paper lined bowl, and cover with plastic.
For improved flavor, consider putting your dough into the fridge after 30 min – 1 hr, and allow it to ferment at a lower temp for a 1 – 10 hours. If you’re in a rush, just let the dough sit a while until it has risen some more.
Preheat the oven and cast iron bowl to 475 degrees. Slash the top of the dough with a razor blade – cut fast and cut deep. Lift the dough out of the fermenting bowl using the parchment paper, and set it down into the HOT cast iron baking bowl. Cover with a lid.
Reduce oven heat to 450 degrees, bake for 20 minutes. Reduce oven heat to 425 degrees, bake another 28 minutes.
Remove the bread from the cast iron baking bowl, and allow it to cool. Enjoy!
Original of the video here