First you have to make your own leaven, Mix 30g of flour and 30g of water in a jar, put the lid on losely so the stuff can get air and feed it twice a day for about 4-5 days on room temperature.
When it comes alive and starts to bubble, close the lid tight and feed it as before but you can now add more, 50 or 60 g of flour and water at once.
If you starve it it will form alcohol layer on top, if/when that hapens, throw alcohol and 50% of leaven away and feed it..
When it looks something similar to this it's ready.
Then if you have stand mixer put 1kg of flour in it and 550-600ml of water depending on type of flour. More water also means better end result but worse dough to work with. Start with 550ml.
Mix it for about 2-3 minutes so it all sticks together and leave it at least 30 minutes, preferably 1 hour.
Add 400g of leaven and mix it again for 2-3 minutes, leave covered for another 30 minutes.
Add 24g of salt, and mix again for 2-3 minutes. Leave for 30 minutes.
Perform stretch&fold and wait for 30min, repeat 6 times. When stretching, really stretch it hard until it almost starts to rip apart.
Put the dough in loaf basket and refrigerate it for 10-12 hours.
Set the oven on highest temperature setting (mine can do 300°C) and put some kind of heat resisant water container on bottom of oven. Wait untill water boils, then put the dough on the grid with baking paper, cut the upside with wet razor and put it in.
Bake it on highest temp setting from 10-20 minutes depending on the type of flour, you want the crust to become nicely brown, not burned, some flours will get burned in 10 minutes some won't after 20. After that lower the temperature to 210°C and bake it so that complete bake time is 60 minutes or there about.
Take it out and cover with wet towel untill it cools down.
Enjoy.