This recipe makes 2 loaves and takes 6 hours total, with 30 minutes of active work
Roughly mix together 620g flour, 380g water, 200 sourdough starter, 10g Salt
Now dump it onto the counter to knead. This process allows the glutens to develop and get more elastic. You know it ready once it is stretchy and doesn’t tear very easily. You may need to find some videos on kneading to get it down, it can be difficult to keep it from all sticking to your hands. Don’t add any flour to your kneading surface at this time. This makes for a more dense loaf.
Slightly oil a bowl and put in the dough and cover with a damp cloth. Place it in a warmer spot to proof (78 degrees F is perfect) and this will take about 3 hours. If it’s cooler it may take up to 6 hours to proof. It should about double in size at this time.
Now take your dough out of your bowl back onto a lightly floured surface to "knock back". Essentially here you need to try to get the bubbles out by folding it over itself while rotating the dough.
Then split the dough into two evenly sized loaves and shape each into balls. These need to proof this way again, this time they need to form a slight skin, so you can dust the surface in flour, place a cloth in a bowl for each loaf (or use a proofing baskets if you have one). Dust with flour and place each in the bowls to proof in the same place as earlier for another 3 hours. After this, they should have a very thin skin, you can put it in the fridge to help it dry out a bit extra if need be.
Now take each out of their bowls onto pans dusted with flour. Preheat your oven to 500 degrees F. Now you can score the surface of your loaves with a razor blade or a really sharp knife. Once your oven is ready, put hot water onto a pan in the oven to steam it and prevent the crust from forming too soon. Place your loaves into the oven for 25 minutes.
Once they’re done, let it cool for at least an hour before slicing. The inside is still baking and might not be fully formed right out of the oven (though sometimes I do steal a side piece or two while it’s still warm)