In a large mixing bowl, measure out 375 grams of warm water and mix in 100 grams of active, bubbly sourdough starter.
Incorporate 10 grams of salt.
Mix in 500 grams of all purpose flour.
Dough will be very sticky. Cover with a damp dish towel and let it rest for 30 minutes.
After 30 minutes, perform your first set of stretch and folds. Continue to stretch and fold dough every 30 minutes until you have completed 4 sets.
By now, your dough should be nice and easy to handle and not sticky. Cover back up with wet dish towel and let it sit for up to 8 hours. At this point you will want to keep an eye on it. Depending on how warm it is in its environment, that will determine how quick it rises. You will want to remove from the bowl when it gets about 1/3 larger. Not quite doubled in size.
Next, carefully stretch the dough on your countertop into a rectangle shape and sprinkle parmesan cheese all over the top. Laminate it by folding long sides into the center and rolling form the ends into a ball.
Continue to build tension in the dough by gently pushing it away and pulling it towards you 5 or 6 times.
Add dough to a floured banneton, or a basket or bowl liked with a towel. Wrap with a plastic grocery bag and place in the refrigerator for 12 hours, or up to 2 days.
You want the bread to be cold when it goes into the oven. This makes it puff up better and easier to score.
Pre heat a cast-iron dutch oven to 500 degrees.
Place your dough onto a piece of parchment paper and score the top with any design you like.
Put your dough into your hot cast iron dutch oven and place back into the oven at 450 degrees for 30 minutes.
After 30 minutes, remove the lid and lower oven temperature to 425 degrees. Bake for 15 more minutes.
Remove bread from the oven and place on a cutting board. Let it sit and cool for at least an hour. It is important to let the bread cool so that it holds its shape.
Enjoy!